Fence post typically rot near the ground, i believe because the repeated wet dry cycle. I have read if using concrete to slope it away from the post and above grade, so this is what i have done. (Actually a 6x6 free standing pergola post i am building, but same concept)

Here is my idea. Does anyone think it would help if i used a product like drylock on the concrete to stop the post from the wet dry cycle near ground level? Will the drylock waterproof the top portion of the post or will it do the opposite and hold the moisture in. How often would this need to be applied outside? Every year? What are everyones thoughts?

Also if it does rot, how long does do you think i can get out of a 6x6 pressure treated post? i am never going to be able to dig up the post which is 4 feet deep wiht concrete so am hoping it last a good 30 years?