Don't despair this can be fixed but it's going to take a lot of patience on your part. First put the collar away for a while, it actually might be part of the problem.Everything you do with the dog from now on has to be under a controlled environment, but make it fun. He doesn't come off lead until you feel confident that you have his full attention. This is a little unconventional for a hunting dog but your situation warrants a different strategy. Think of him as a good companion dog and work on that first, the hunting WILL come later. Start training him as an obedience dog and throw some hunting skills in with that training like working with birds. While walking with him ALWAYS return the same way you went and let him lead on the way home, he'll be using his nose to get back to your home/truck. Take a walk with a friend or wife/kids and let them hold your pup while you jog away and hide a short distance away. Then let him track you down while still on the lead, praise the heck out him when he finds you, make it a great fun game, again through some bird hunting skills in when you can.You and him need to develop that special bond that makes him want to be you more than anything else, take him with you when ever you can, be it to the store what ever, soon he'll whine when you leave the house without him and when you do let him off lead he'll be checking back to see where his buddy is!