I am building a fence on flat ground. The water table is very high. We dug 2 1/2 ft deep holes and they are now about 3/4 full of water. I am putting in 4x4s and 6x6s(pressure treated). My question is that is cement(and will it set up, I have heard various opinions) or rock better to pack the posts. I am putting a 48' fence, and 3 "T" posts to every wood post at 10 ft apart. Also, is 2 1/2 ft adequate for the depth? Any ideas?