I have one customer that I cut grass for, and a lot of the heads in his back yard stick up and don't go down unless I tap it down. The back yard system was installed by the previous homeowner. Rainbird heads. I swear I have hit probably 7 heads this year alone just in the back yard. He waters to much, grass is long and I don't see them until they go flying. What could be the reason they are staying up? Thanks.