Some  rotor style sprinkler heads tend to stick up out of the ground after the system runs - especially early in the watering season. All you need to do is step down the sprinkler head. With gentle pressure from your foot the head should easily retract back into the ground. The older the heads are the more likely this is to occur and some models are more prone to sticking up than others. There isn't a lubricant or anything to apply to make that not happen. We recommend folks just remember where their sticky heads are and to step them down before they mow as long as they are actually doing their job properly there is not much point in replacing the head until you accidentally decapitate it with your lawn mower.