Last year my Brother in law came back from a days fishing to find his whole trailer stolen. He did have the safety chain padlocked to the towbar, but they just used bold cutters to cut the chain.
Quick phone call was made via the mobile, I take my boat off my trailer, drive to the ramp, put his boat on my trailer, go this his place and take his boat off, return home and put my boat back on my trailer. All up a very time consuming job, but these things have to be done in a time of need. Plus in the 90 minutes it took me to get to the ramp he went fishing again and catches some very nice fish 100m from the ramp.
I often use Nudgee Creek boat ramp, but I will never leave my car there at night due to being so isolated plus the ground is always covered in glass from broken windows.