What deck sealer should I use?

[cosmo20002]

Assuming that the deck is fully exposed to the weather, seems to me like they all suck. The shitty ones, you need to re-do every year. The "good" ones, you still pretty much have to re-do every year, maybe two.

It's even worse if the deck is mostly in the shade cause that water will get into every crevice and won't dry out normally. Speeds up the wood rot considerably.