Oh yes, I have heard of this before. That a protector is 'assigned' to the practitioner before starting them on their practice. I was attracted to Dorje Shugden before I know much about protector practices or Buddhism. I have been told that due to the degenerating times, we have lots of accumulated much negative karma that will distract us from our Dharma path hence a protector is very good in helping us clear our obstacles and bring positive results during our practice. The best part is that all protectors are Enlightened beings who are emanation of Buddhas and Bodhisattvas. 
Hi Bambi.. I would like to correct you on one thing... not all protectors are Enlightened Beings. Nechung the principal protector divinity of the Tibetan government and the Dalai Lama is NOT an Enlightened Protector. Enlightened Dharma Protectors are manifestations of Buddhas, and Dorje Shugen an emanation of Manjushri is one!
And amongst Protectors, there are Common and Uncommon Protectors. Common Protectors being Protectors that protect the Dharma/Buddhism in general and Uncommon Protectors protect a specific teaching or lineage. Dorje Shugden arose as an Uncommon Protector in order to safeguard and protect Tsongkhapa's teachings but does that mean Dorje Shugden wont help outside his so called realm of protection? Of course not... because Dorje Shugden is an enlightened being.
I found an interesting except from HHDL book "Freedom in Exile", that mentions the unique relation HHDL has with Nechung:
"For hundreds of years now, it has been traditional for the Dalai Lama, and the Government, to consult Nechung during the New Year festivals. In addition, he might well be called upon at other times if either have specific queries. I myself have dealings with him several times a year This may sound far-fetched to twentieth-century western readers. Even some Tibetans, mostly those who consider themselves ’progressive’, have misgivings about my continued use of this ancient method of intelligence gathering.
But I do so for the simple reason that as I look back over the many occasions when I have asked questions of the oracle, on each one of them time has proved that his answer was correct. This is not to say that I rely solely on the oracle’s advice. I do not. I seek his opinion in the same way as I seek the opinion of my Cabinet and just as I seek the opinion of my own conscience. I consider the gods to be my ’upper house’. The Kashag constitutes my lower house. Like any other leader, I consult both before making a decision on affairs of state. And sometimes, in addition to Nechung’s counsel, I also take into consideration certain prophecies.
"In one respect, the responsibility of Nechung and the responsibility of the Dalai Lama towards Tibet are the same, though we act in different ways. My task, that of leadership, is peaceful. His, in his capacity as protector and defender, is wrathful.
However, although our functions are similar, my relationship with Nechung is that of commander to lieutenant: I never bow down to him. It is for Nechung to bow to the Dalai Lama. Yet we are very close, friends almost. When I was small, it was touching. Nechung liked me a lot and always took great care of me. For example, if he noticed that I had dressed carelessly or improperly, he would come over and rearrange my shirt, adjust my robe and so on.
"Nechung has always shown respect for me. Even when his relations with the Government have deteriorated, as they did during the last few years of the Regency, he invariably responds enthusiastically whenever asked anything about me. At the same time, his replies to questions about government policy can be crushing. Sometimes he just responds with a burst of sarcastic laughter. I well remember a particular incident that occurred when I was about fourteen. Nechung was asked a question about China.
Rather than answer it directly, the Kuten turned towards the East and began bending forward violently. It was frightening to watch, knowing that this movement combined with the weight of the massive helmet he wore on his head would be enough to snap his neck. He did it at least fifteen times, leaving no one in any doubt about where the danger lay.
"Dealing with Nechung is by no means easy. It takes time and patience during each encounter before he will open up. He is very reserved and austere, just as you would imagine a grand old man of ancient times to be. Nor does he bother with minor matters: his interest is only in the larger issues, so it pays to frame questions accordingly. He also has definite likes and dislikes, but he does not show them very readily.
