Be careful, Don't let this happen to you

Back in the 80's my Dentist friend was working under his DP. He had it aired up to provide more room to work. I am not sure what he was installing but it involved using a drill underneath the coach. Apparently he hit an air line and the coach came down. It did not kill him but it cut off the blood supply to his brain long enough that it was like having a stroke. At 32 years old, his career was over as a dentist because of permanent nerve damage that affected his arm and hand movement. In an instant his life was changed and he never recovered from the physical damage and financial loss.
Do not use concrete blocks, rely on your leveling jacks, or anything else that is subject to failure while you are under the coach.