Discipline your dogs when they chew the collars. Its called raising dogs. Never let them start with a bad habit. you have to be on them 24/7 and be consistant (just like raising Kids), then when they are older dogs you dont ahve all the crad to deal with. Its like starting to teach a kid when they turn 17. too late.
GET a sprayer put some water and listerine in it, when the dog starts chewing on the collar, you in a command voice say to it, NO, then if it doesnt stop you spray in the snout, (not to worry it wont kill them even if it sprays in the eyeballs). BUT it will soon teach them to listen to your voice.