Yellow lab litter mates (brothers)

Question
I have two 1yr old pure bread yellow labs.  they are brothers from the same litter.  We have never been able to keep collars on either of them because they chew them off of each other.  We have gone through at least 10 sets of collars.  Is this normal?  Can it be stopped?

Answer
If the 2 of them are allowed to play constantly, it doesn't surprise me.  It might be safer not to insist on them wearing collars.  Dogs have gotten their jaw twisted up in a collar and even choked the other dog to death.  In one of my tours of the dog guide school kennel, I realized each bay had at least one set of bolt cutters handy, hanging on the wall.  I asked, and was told it was in case of a dog getting its jaw caught in another dog's collar.  They never had a dog injured that way, but a few trainers were separating them.  

Collars are important to hold identification and some states require rabies tags.  Having the dogs microchipped would help recovering them if they got loose.  Not sure what to say about the tags.  They shouldn't be able to chew through metal slip collars, but they are even worse as a choking hazard.