what did gray bever have to make to in sure that white famg would not come back to him

Grey Beaver made White Fang a thong (collar).

But scarcely had he lain down when Grey Beaver staggered over to him and tied a leather thong around his neck.  He sat down beside White Fang, holding the end of the thong in his hand.  In the other hand he held a bottle, which, from time to time, was inverted above his head to the accompaniment of gurgling noises.