My chickens never were fooled by golf balls either, am always surprised it works for others. If there's a golf ball in a nest my hens look at it and say "I ain't going in there with that.....THING!". Even if I leave it in for weeks, just one or two hens will use that nest occasionally while the other nest boxes without golf balls get filled up with eggs.
I used to have some pheasants that were egg eaters. One solution is to get lots of eggs and just put them all over the coop. Let them eat all the eggs they want.. eventually they will get "bored" and not be so ravenous about eating every single egg. Also give treats and things high in protein, in case they're hungry for protein.. I gave the pheasants cat food and lots of eggs. It worked well for these pheasants..
I suggest hard boiling store bought eggs before giving though.. reduce the risk of introducing salmonella into the chickens. I do suggest cat food if they're only getting "layer feed".. maybe also adding turkey/gamebird feed that's higher in protein to the mix and see if all that helps.
Fake eggs should work well, get a lot.. leave several in the box and a couple around the yard too- get them bored with the appearance of eggs too?
