Some shops use heavy steel pipe about 8" to 12" diameter at about a 45 degree angle going into the ground. At the shop I worked for they had it installed when they built the building. We had padding on the inside for a short way so if the gun bumped the inside of the pipe it would not hurt the gun. The top was covered with a piece of rubber with a slit in it to help keep the noise and smoke in the tube.
Just walking on the edge of of my grave.