you guys are funny
I would be careful with that foam. It tends to looove slurping up as much water as possible... Cant say I have a better foam in mind other then marine expanding foam... but its expensive and powerful enough that if you added to much you would end up detonating the decoys into a giant ball of foam.
Or you could stuff a balloon or something into the decoy through a hole strategically placed near the anus and fill THAT with the foam to keep it out of contact with the water thus prolonging the life of the foam as long as you don't poke more holes in it with little steel balls while they are bobbing in these wave things.
I do think that patching the holes with a crappy blowtorch and milkjug plastic and installing a drain plug of some sort would be a good solution as you could drain them and re-patch... and repeat if they keep springing leaks.
Being allergic to fish... I cant eat fish ducks for the same reason I cant eat shitty cheap chicken... alot of its protean comes from....
Fish.
And as such. I don't shoot ducks inside my friends decoys ( anymore ) or fishducks.
SHould find some old black wood commercial net corks. and toss them out of the boat on a rough day and practice timing blasting them. Same idea people shoot clay pigeons etc. Shooting out of a boat is a skill that gets better with practice.
Eat your dessert first.
I foam my sea-duck decoys as well, another reason to foam them instead of just patching the holes is the fact that some holes are very hard to see. The best material I have found to patch holes and repair foamers is urethane windshield glue, it is black, flexible and hold very well.