ecollar is a very expensive piece of equipment to possibly get bit/broken by a dog. I believe most are plastic so I can really see a dog biting down and breaking the thing. Other than that I really don't think there is a danger other than what you get with other collars. I'd never let a dog play with a prong on or a choke on, if the other dog gets caught in that collar it might cause some issues due to how those work, but with an ecollar I could just see an expensive broken tool if the other dog bites down on it a bit too hard.
CD RE TC HIC 7/10