So I just got the mesh stapled onto the window I cut in the coop, and today I put up my chicken run. For most of it I used an existing fence, wall, tree, and the coop itself, but I did have to sink one post. Pounding a post into clay is not much fun, and I'm a very lazy person. Here's how I dealt with it. After digging as far as the shovel would go easily (about 6 inches in this clay) I poured in a couple liters of boiling water. This reduces the clay to soft mush. Cold water won't do it, it's got to be boiling hot. Then the digging is much easier although of course the hot mud won't set around the post until later. Two repetitions got me a hole about 18 inches deep. (If the post doesn't stay still tomorrow, I'm going to put in a foot of Quick-Crete and that will hold it). To remove a stubborn post or tree stake (especially the kind with the knobby bumps on the end) simply wiggle and twist the post while pouring the boiling water. Then the stakes come right out in minutes or even seconds no matter how long they've been in there or how hard and clay-like the soil is. I came up with this trick years ago while doing landscaping one summer, and used it to get my all-female construction crew to out-perform the guys. We were pulling out tree stakes and did six in the time it took them to do one. They were pitching fits, thinking we had softer soil or something. So we swapped, and kept outperforming them by the same ludicrous rate. After yanking and twisting on those stakes as though they were about to strain something, but seeing us toss a stake into the pile every couple minutes, they were starting to question their masculinity. After an hour or so of very good fun I took pity on them and shared the secret.