Cindy's Answer:

That's a really unfortunate situation that you are in. For the future, DON'T let anyone else use the remote collar on your dog. Don't even have the collar available. If someone else watches my dog, I don't give them the collar and the dog MUST be either on a long line or in a secure fenced-in area. I don't want an accident with my dog getting hurt but I'll admit I never even thought about someone using the collar in the wrong way. I would be very upset if this was done to my dog.

I think all you can do is start from scratch, don't allow him to avoid getting the collar on. Put him on a leash and then matter of factly put it on. Don't ask him to come to you right now without a line on him. Start like he's just at the beginning stages of the collar conditioning, I'd make him wear it a LOT without using it.

Do NOT call him when you don't have a way to reinforce the recall, if he doesn't have his collar on, don't call him. This is the most important part. He may be wearing the collar every day for a very long time, don't get in a hurry to "test" this.

My fully trained dog wears his collar every single day when we go outside on our unfenced acreage, smart dogs learn in one repetition that if the collar isn't on there is no consequence for not recalling. I like to be ready for the unexpected.