I'm installing a wooden fence around my back yard using prebuilt cedar panels and 10 ft (3+ m) 4x4 pressure treated posts buried 3 1/2 to 4ft (1+ m) deep. The posts are packed in with pea gravel to allow for drainage.
Most of the post holes I've dug go through 2 ft (60 cm) or so of hard clay before hitting a softer sandy soil. On one corner of the lot however, the hard clay continues down the full 4 ft. I placed a few feet of water in a hole to try to loosen the soil for digging (which helped greatly), but after 48 hrs the water level had only gone down a few inches.
What can I do to get these post holes to drain properly?