Our Continental O470-U engine has a locking dipstick. It works like a champ; you just gotta know how to unlock it.
If you don’t unlock it and just pull it out (like the other two planes), you risk pulling the entire tube out of the engine. (It’s happened.) This will require a trip to the hangar for repairs.
These three pics are pretty self-explanatory. You just rotate the pull-ring until it unlocks – and reverse the process when complete.