I'm not the best person to answer, since i have just gone through FF for the first time. But When i gave my dog the firm "NO" and then "HOLD" I also held his mouth shut very tightly with the bumper in it. And i would repeat that everytime he droped it. When he would loosen up I would just cuff his chin and give a firm "HOLD".
When you start to apply pressure and give the "FETCH" command. You need to have a good grip on your dogs ear and collar. Even if he/she tries to lung forward don't let her. You want the dog to try to do it though, because that means that they are learning what your teaching. But in order for the FF to work, You have to apply pressure and the dog has to understand that the only way to stop the pressure is to make the retrieve (get the bumper in her mouth.) My dog tried to pull away and get the bumper before the ear pinch, but i had to hold him back a little even with him pulling on the collar. I wouldn't let him go forward until i said "FETCH" I don't pinch his ear until i say "FETCH".
After i started with the pressure part of the FF i havn't had any problems with him holding the bumper firmly. because he knows that as long as that is in his mouth, his ear dosn't hurt.
I'm having so much fun with "HOLD" now, he brought me the paper this morning, it ways as much as a goose and he carried it in to the kitchen and delivered to hand.
Keep trying, I was soooooo frustrated. With good advice from the other guys on here that have gone through the proscess a couple of times, it really helped me. And i got through it.
.....you've got to ask yourself a question: 'Do I feel lucky?' Well, do ya, punk?
Die' en ain't much of a livin' son.