Before going after it with a long bar, I'd have a buddy hold a 4-6 inch length of solid 1/2 inch steel rod on the head of the bolt with a pair of Channel-Locks while I gave it a good beating with a BFH. If you just go after it with brute force without trying to break the corrosion connection with vibrations, you stand a chance of twisting the bolt off at the deck. Just my opinion.