Frank,
I forgot the two most important tips of all and it could help you in the liability department. First, always do a careful search for utilities and/or underground hazards (rebar, trash, rocks, sprinkler systems, outdoor lighting, etc.) Dig all around the stump. I carry a hacksaw, several different sizes off pipe, couplers and pvc glue to repair sprinkler systems I accidentally hit. Ask the homeowner or have a marking service come out to locate utilities (should be a free service-Texas has a toll free number for this service). Most utilities should be 18" but not telephone, cable, sprinkler or outdoor lighting-that stuff can be anywhere.
Second, carry 3-4 sheets of 1/4" plywood and some T-posts to hold it up in a wind. I put one 4x8 sheet on the ground directly underneath my grinder because its easier to use a grain shovel (Yankees call them snow shovels) on a hard, flat surface. Also, you will need to pivot off this sheet. Next, I stand two sheets up on either side of my grinder because the grinder tends to shoot stuff out the sides. Lastly, I cover any windows or fancy landscaping. I painted my logo on the sheets for some free advertising.
Yes, its a pain in the ass to carry around 3-4 sheets of 4x8 plywood but its not that heavy. I also carry one sheet of 3/4" to get up curbs and over obstacles.
If you do all these things, you may not need insurance, especially if you only grind parttime. Just my 2 cents...
Most handlebar grinders allow you to adjust the angle of the handle to keep the cutting head down on the stump. I keep mine a notch lower than most folks just to keep the weight down on the stump. I've watched guys grind with the handle up in the air and their arms over their heads trying to pivot. I just think I'm smoother through the cut with the handle a little lower. Then again, I'm five foot nothin' so adjust it to your own height.