Some years ago, a few years before the Schengen agreement came in, while living and working in Germany, I had a project running in Lisbon. Frequently, I would drive down there. One day, thought I would take my wife and son as I was going to be there for 5 to 6 weeks. The wife being Filipina, needed visas so first I obtained the Portuguese one for her and she then applied for the Spanish visa. It was only a day or so before setting off that I noticed her Spanish visa was for a single entry only. This was not going to work as, in order to drive anywhere from Portugal, you need to enter Spain from France on the way out and re-enter Spain on the way back. So, we drove there with no problem. Didn't bother with the Portuguese border officials crossing from Spain into Portugal; I just gave them a cheery wave. When it was time to return, I chose to leave Portugal via a very quiet border post I had sussed out. We stopped in a cafe about 100 yards from the border post and had a nice lunch while sitting on the cafe terrace. As expected, at lunch time all the Spanish officials disappeared inside their post for lunch. We all jumped in the car and went "wheee" right through a virtually abandoned border! The Spanish consulate in Frankfurt knew we were driving as that was stated on the visa application but were not smart enough to figure out how one could do the round trip with only a single entry!