Every sentient being is responsible for his own actions, this is the Law of Cause-&-Effect, Karma. If performed virtuous deeds with virtuous intentions, you will be rewarded with happiness in future, in this life or in future existences, in proportion to impact of your virtuous deeds which some call the ripple-effect or butterfly-effect, and vice-versa for non-virtuous deeds. In this sense, all sentient beings in Samsara have their own 'Karma Balance Sheet', virtuous deeds are like 'assets' and non-virtuous deeds are like 'liabilities'. It is up to us to accumulate merit and purify our negative karma as much as possible while we are still alive.
Buddhas, who have already achieved perfection in Bodhichitta, cherish each and every sentient being in Samsara like his one and only child. Yet despite this perfect love, which is way more superior than worldly love, and their spiritual powers, the Buddha is not the creator of the principle of Karma, nor can He exert any form of influence over it, this truth has been illustrated in many stories of the Dharma. Hence He can't stop us from experiencing the results of our non-virtuous deeds which we have created for ourselves, if he can do that all Buddhist will not experience any form of suffering in our lives.
What He can do is to educate sentient beings of Samsara the principle of karma, so that sentient beings will not be ignorant of it and bear this principle in mind. After understanding this principle they will take care in all deeds of body, speech and mind. This 'purifies' the deeds of body, speech and mind of ignorance about Karma.
Whatever that's good, carry on to do more and improve it
Whatever that's good which you have not done, start!
Whatever evil that has been done cannot be undone, but try not to do it again and make things worse
Whatever evil which you have never done before, please don't start!
If sentient beings can believe and uphold this, then this will be the start of the said 'Protection of the Triple Gem', because we are putting in the action the advise which we have received from Buddha himself.
A simple analogy would be this:It's like as if we are always in debt, having no savings, and not having enough money to fulfill our dreams. Then a financially savvy friends comes along and gives you advise on how to control your spending, starting a savings account and getting a better-paid job. After following his advice, our financial life change for the better.
If you continue to do and improve on the virtuous deeds which you are current engaging in, your merit will grow and so is the prospects of enjoying happiness in future. Hence you are 'protected' from the fate of not having accumulated enough merits for happiness in future.
If you start perform virtuous deeds which you have seen others do and haven't done so yourself, you are 'protected' from the misery of missing out on the kind of happiness which the deed can bring for you.
If start apply the four-opponent powers of purification in all your non-virtuous deeds and start making up for your past wrongs, you are 'protected' from consequence of continuing your mistakes, making old enemies(karmic debtors) having reasons to hate you even more and become more determine to harm you, and making new enemies. You may even convert an enemy into a friend in this process.
If you never committed a particular non-virtuous deeds, you are 'protected' from experiencing the results. This is because the teachings on Karma states that you cannot experience the result of a deed which you have never committed, virtuous or non-virtuous.
It is only when we follow the advise given by the Buddha, then we are protected. If we don't and continue to do as we please, selfishly harming others for our own benefit, faith alone cannot save anyone. It is just like having faith in a doctor and not taking the medication which he had prescribed for our illness, we will ever be cured.
I do understand from sources that demons and evil spirits can stand being in the presence of blessed statues or thangkhas of Buddhas/Bodhisattvas/Dharmapalas (Supramundane ones like Dorje Shugden, and righteous heavenly beings), High Lama (or even an ordinary monk who has been upholding his percepts purely), or if you are having on your persons a sacred object. However this does not solve the problem, because we yet to do anything to resolve our differences with our Karmic debtors, that means they still hate us and wants revenge! To me, such protections serves to buy us some time to figure out what to do and do it. It is like in our lives, some people may hate us due to some reasons, but can't touch us because we are in an advantageous position. I am sure they are going to focus the first chance they get when what stops them is gone, even temporarily. Hence we should desire a long term solution to the problem.
I have done much evil in the past when I was less learned in the Dharma. Now I am trying to understand more and practice whenever I can. I am trying hard not to repeat my past mistakes as much as possible. Yet my past still comes back and haunt me every now and then. I have great faith in the Triple Gem, I do my best to learn as much as possible and integrate them into my life, but my life is not problem-free despite being able to write this. However if I hadn't follow Buddha's advice, it would have been much worse. Even for the ordained, they have to deal with their karmic debtors too, although it is easier and faster for them to repay their karmic debtors since they are under the daily tutelage of their Gurus on this matter, and their daily lives are occupied with Dharma practices ( not like us,we have to find time to do Dharma practice), the merits from which can be dedicated to Karmic debtors.
By the way, from my own experience, you must specifically dedicate merit to your karmic debtors in order to see results, you need to specifically mention this when you are dedicating merits. I used to think that after engaging in so much Dharma practice and doing many charitable deeds, my karmic debts are automatically clear even without consciously knowing or thinking about it. Then to my horror, I realized that it doesn't work this way.It is just like if you are in a good profession and earning a high income, but you have forgotten that you owe a friend some money, and he is still angrily waiting for it.
Being able to learn and apply the Dharma is the real protection.