Background
My wife and I rent an apartment and a garage. The garage is on an underground parking underneath the building in which we live.
The garage has a metal door which we lock with a key. The underground parking has a lot of parking slots as well as garages like the one we use.
Now, what is frustrating to us is that there is someone who often urinates just next to our garage door. There is also a car in the slot next to ours, but its owner seldom uses it (it's covered in dust), so it is improbable they would ever notice this.
The parking is always cold, being underground, and so it's always wet and smelly. This behaviour happens often, but we've never caught whoever is doing it. Last Friday we went to the parking right after it had happened and found it very gross. Obviously, something should be done to deal with it!
We're convinced the offender is someone who lives in our building as the parking is only accessible with a key or a remote control.
But we're not sure how to approach this and get results. We can contact the owner of our apartment but he doesn't live here, and we wouldn't want to bother him with something like this. There are also no cameras in the parking.
We were thinking of printing several notes and sticking them in the parking as well as in common areas like the building lobby and the elevator, but we can't think of a text that wouldn't come off as passive-aggressive and thus would cause the offender to continue.
Question
If we were to communicate with this person through a note we print, what should we say to them, so we encourage them to stop what they're doing?
Or, can you suggest an alternative approach to pass the offender the message they can't continue urinating right next to our door?
My location is Bulgaria. The described behaviour is not considered OK here.