We did that several moths ago, his wife was doing all the driving. She was supposedly taking a nap when he decided he need to get his prescriptions filled. He took the keys and managed to get the pharmacy to get his prescriptions but got lost on his way back. Now we have the problem of telling is wife we are taking the car away from her as well.
This is my wife's dad. There are six brothers and sisters that are all very successful and huge control freaks. Thankfully most of the siblings are starting to get on the same page now they see how bad it is and how bad it could have been.