Hard Mouth thoughts

Well there is so much back story but I will to sum up. I need some thoughts from those experienced at dealing with hard mouth. I have been working with a GSP (Upland work) on and off for a few years for a client. The dog is highly NAVHDA bred GREAT pedigree and has a ton of drive, extemely friendly with ALL other other dogs and people, was easy to steady on point and handles through a needle for me. He will honor points and retrieves and I tell you this to tell you his assets. :)
But he has been hard mouth on birds and I can personally just barely keep it managed with extreme attentivness. He is FF with ecollar overlay. With bumpers He calmly chews on a hold and I finally last year overlayed a nick nick on each chomp qnd he will stop and hold correctly but this has to be maintained A LOT. On birds he munches Hard at first pick up and then slows with correction to where he gets managable.
Trouble is he is a client dog and they just are not nearly attentive enough to keep this dealt with. Believe me I have tried every trick in the book with this. The owner is well known for making close shots on quail (which mangles them) and this worsens the issue.
I am to the point that I am considering reccomending he throw in the towel on this dog. The dog needs a handler who is attentive and ON TOP of the issue.

Do you think I am off base here? Is there anything else I could possibly do here? Any detail that I might be overlooking. About at my end here and that is rare for me. I hate failure!
Any thoughts are much appreciated.

ive never done it but ive heard of people using a hard wired brush????

How was this dog as a pup? Who did the force fetching?

I did the FF. He was a nice natural retriever with bumpers clean to hand. BUT he chomped on them. Its not easy to see with bumpers. HE doesnt toss or roll or anything. Just squish squish squish.
Keep in mind this is a birddog. The bird retrieving was always bad so we did next to none until the FF. The only reason I did the FF was Because of the hard mouth. We spent almost 2 months!!!! On hold and carry. I can control it/ stop it with both birds and bumpers but it come RIGHT back if he is not held to it constantly.
also tried all the brush and wire and every other thing. He just knows they are different things.

The single most helpful tactic seems to be very frequent drills where I make him hold a fresh killled quail for long stretches. Like 10 minues on a whoa and hold.

I think you have some tough sledding ahead.

Trained with a dog once who would sort've flatten birds, he used 2 chomp, when that was corrected he learned he could flatten, much harder to watch for. Something that worked and that the owner was able to maintain, was to shake up a coke and make him carry that around, if he got to tuff, it'd spray him in the face which is unpleasant. Anytime the mouth issue came back about dog had a little session with the coke can and became very mindful of the pressure he was exerting with his mouth. The owner was a little surprised when three 12 packs of coke appeared on the his training bill, & he buys off brand now ;)

I'm curious if you really got a good Hold ingrained first and stayed on that part of the process until truly proofed. HOLD = Stay for the mouth.

Very! He will hold nicely for 10 minutes, will carry around, he will stop this munching when corrected. But I have to watch to correct promptly. Its fast and hard to time. I could maybe video it. Its maybe 2 chomps per second and rythmic and he will stop with the nick but you have to SEE it. The owner does not catch it. With birds (quail are small) one hard CHOMP and its squished. Even if I correct and stop it its too late really. So then he gets to hold the squished guts falling out bird for several minutes and he does not munching again and releasing to hand.
However I do think that the first stages of picking up and returning are the worst. Maybe I need more focus on pick-up? Maybe there is a piece there that I could prevent the chomp somehow. I do pre-cue HOLD as he goes to pick up but I still have to watch for a chomp very closely.

Hunt em up, hmmm havent tried that. Interesting.