[Mr. 16 gauge]

If you are going to use a collar, you need to get a book and read it first. You also have to make sure that your dog knows the command thoroughly before you zap him with the collar for breaking/disobeying/ignoring the command.

I agree 100% with Fabs' statement.....a lot of good dogs have been ruined by the use of electricty & a short sighted understanding.

.....but let's face it; hunting season is almost over, and E collars are expensive. You say "he does pretty good, but he goes to other dogs to sniff and play".....sounds like he 1.) might still have some puppy in him and 2.) doesn't really understand what the commands "come" and "stay" mean.......they mean "come....right now!" and "Stay....don't move!", not "come....when you feel like it" or "stay.....if you feel like it".
These sound like simple problems to fix, esp. since the off season is near, and you can focus on the behavior while not hunting. Take him to a dog park on a long lead and when he shows interest in other dogs, tell him "Stay" or "come", and if he doesn't obey immediately, give him a pop on the lead and repeat the command louder and sterner. I really think that if you do this, you can correct the behavior w/o having to invest in a collar.
....don't get me wrong, I don't have anything against a collar; I just think that they need to be used judiciously by someone who knows what they are doing.