you have to be next to the dog to change the number,if you have say number 12 and some one has a 2/22/32/42 it will interfere.when you see this try to catch up your dog and change numbers. you can enter random numbers and scann an area btw.5 garmins would cover all numbers i guess....if your paranoid you could change your number a few times during the hunt
He had the dog and collar in his hand