The first step we took was to try and find a product that would give the decoy paint a protective finish without a lot of glare. After spending a considerable amount of money and trying a lot of products, we found a product that has worked extremely well for us to provide a protective finish without a tremendous amount of shine or glare. (One thing to keep in mind about real ducks on the water, on sunny days they give off a natural sheen because of the water and feather oil, so don't be too concerned it you have some shine to your decoys. It will look natural on the water.) The product that we use is: Krylon 1311 Matt Finish that can be purchased at most Wal-Marts and home improvement stores.
Typically we will spray our decoys with 2-3 light coats of the Matt-Finish but if these are decoys that will get a lot of abuse (i.e. carried in bags, tossed into boats) we'll give them up to 4 coats.
Found this on the net... Hope it helps.. Ed