You could also work on using cover when doing weapon presentation indoors.
I have seen our range under water twice in the last 32 years I have been on the Board of Directors. Ours will be drained off in a matter of hours. I would go nuts having it covered in water for two weeks. Our problem with flooding is the Trap Houses going under water. Big Potentially Expensive Problem. We now run a dozer down the dry creek bed every few years to get the debris out. This stopped the Range flooding problem.
I have never seen the grass that tall on our range either. I have had to mow the range twice in about a week however.
Shooting in the rain might not be all bad. We had a drizzle coming down a while back during a 600 yard F Class Match. No Mirrage, and No Wind. We had our first 300 with 23 X's shot on the range that day. We do have a nice covered shooting line, so the shooters were not getting wet. The target crew were the only ones getting wet that day.