Use articulated risers when installing pop up sprinklers to ensure you get the pop up finished at the correct height. An articulated riser articulates or pivots to allow the pop up to be set at the correct height regardless of pipe depth. It will also partially act as a shock absorber if the top of the pop up is driven over, allowing some give and reducing the stress on the pipework below.
Articulated risers come in various sizes and lengths. It is important to try and match the riser diameter with the inlet diameter of the pop up.