Excellent job Haywood, Sonotubes make great columns,
I used some of the 10" tubes for the columns for my graveyard fence. The only problem with them is that the size isn't consistent, just because it says it's 10" doesn't make it 10". I had to measure the diameter of each tube in the store to get the ones I bought to be approximately the same size.
You might try putting in some stakes to set the prop on. That way you can raise it above the grass. Try it some where you don't care if the grass dies and see how long the grass can survive.
Killing the grass isn't a problem here, the draught has already killed it all. At least if I need some open graves I can just dig them.