Another thing I did with my dog, when he was on the table, reinforce the hold command.
Put the bird in his mouth with a fetch command, give the hold command and every time he moves his mouth or chews, smack the dummy and make it move. He will drop it a few times, but will start to hold the dummy firmly, but not bite it, in anticipation that you will hit it. If he drops the dummy, immediately put it back in his mouth after a stern “NO”. They pick it up very quickly that they do not drop a bird.
Take the hold command and bring it outside on the check cord, and make short throws, fetch and then hold commands, bring him to heel, and make him hold for a couple of minutes if necessary. Make sure he knows that you do not drop a bird until you give the command.
I often times reinforce this in the yard, by making him carry a dummy around at heel for a couple minutes at a time. Now when I throw a dummy, he automatically goes to heel and sits with the bird in his mouth and waits for the give command.
Good luck, training is a very rewarding experience, but also has some really frusterating days.