Brian (Titanium) has given some excellent advice, overlapping what I said and providing a lot of added details. Having grown up in North Dakota, being one of the first in Alaska to install large C-band dishes in the 80s, and working around the world in a great variety of climate conditions, I feel fairly qualified to make suggestions. Here's one that I learned the hard way in Seward, Alaska. I was fighting with a 12-foot Paraclipse and about 8 feet of pipe above ground, assuming I could dig a four foot hole. I hit solid rock everywhere at about 30 inches, and it was not particularly level, and I did not have a jackhammer to modify the hole. So I foolishly poured the cement, and added a little lip to the outer edge of the pour, hoping the added weight would increase the stability. To my surprise it ending up working like an inverted egg. You would shift the pole off plumb by at least 5 degrees or more every time that you motorized from 139 to 91 West (our view from there). The weight of the dish would mess up the pole, and it would literally shift like an egg out of balance. After a month of attempting solutions, my customer found a friend a few miles away that was interested in C-band (this was 1984), and took it off his hands at most of the cost. I donated my labor to align the new installation (new owner took the pole out and installed it in a more suitable location), and my reputation was salvaged. The thought of you attempting to correct things with solid rock jogged my memory, and while you will have better results four feet down, pay attention to everyone's advice and err on the side of caution.
Heavy guy wire cable with suitable turnbuckles (3 or 4) to balance the pipe would be a suggestion I would add, but make sure that if you need to go there, it is done before the ground freezes. Additional outriggers can be less than reliable if put in at the advent of freezeup. Good luck!
