I rent two from the Council, they are very close to where I live, in a small cul de sac opposite my home -- so I often see everything that is going on !! Everybody around here knows we have three cars between the two of us and think we're mad anyway !
Extra double padlocks help deter the low life and to be honest it's not too much of a problem in this immediate area.
( Having said that the one time was about 8 years ago - the 80 was away having some work done so they could see/access the five 7x15 108 pcd Ronals and the four 6x15 100pcd Ronals once they had levered the door open, and they took the lot ).
I pay about £46 month for each garage...... it does add up !