If you run over the head it will tear it up. I usually tell the customer to mark the heads, but on a couple last year, I had them turn the sprinklers on and put a marker where they were.
What will be interesting this year, is the invisible fence for dogs, seems everyone has them.
I always ask the customer if they have them when I give them the price. I also will offer to give them flags to mark them (cost like $1 for 10) so we can avoid any damage to them. better to prevent the problem, then pay to fix it!
And yes, and aerator will tear up the spinkler head if you run it over and try to get a plug out of it!
Any one ever seen a rain bird 9" head on a golf course get hit. It look like a fountain in the middle of fairway. Not a good day, i glad it don't work there anymore. I tell customers when i will be there and give them the flags to mark the system themselves. Plus if i do hit a head, its their problem since they didn't mark it.
Also mark the valve control box. Hit the edge of one last year and pushed it down on the pipe and spit the pipe. Like the Bev. Hillbilly's , just not Texas Tea. I give them the flags a few days before and just pick them up when I'm done. The no-see-um dog fence is a lot harder to deal with. I know where my weekly customers are and I will do them but I avoid the one time plug deal if they have a fence. Most don't know where the twisted line is that runs out to the fence and that is hard to find if you hit it.(and you will).