Putting up a horse fence, and have a long line where I hit clay at each hole. the bushhog auger seems like it has plenty of power, but the bit only goes in a few inches, and then the hole has to be dug by hand to breakup the clay in the hole. taking about 30 minutes a hole. No rocks have been found. Is there a particular technique that eluding me? Can I put a different tip on the bit, to pull the bit in more aggressively?