We have a terrible parking situation in my condo-complex.
People parking in reserved spots and blocking access to garages all the time.
We had to get special signs installed then hired a security company to patrol the complex multiple times each day. At first they were 'booting' cars to immobilize the offenders. Now they are being towed.
One or two people get towed and word spreads that you mean business.
Sure it might be expensive for the person to get their vehicle out of the impound lot, but I wonder how much you are paying for that nice garage that you are not guaranteed access to.??
Oh yeah!! How did it feel when you hobbled on your bad foot to keep them from feeling the pain to their wallet? I was pretty peeved a few years ago when I was in chemo treatment and had to drag my bald little head half way down the block to park because someone was blocking my garage. Couple of my neighbors made sure that that particular person didn't do that no-no again.
People often don't make change until their behavior starts costing them money or extreme embarrassment.
Once this starts happening to your 'visitors' you most likely start to see the clear path to your garage.
-Aude.