Yep…and even that might not be enough.
Mine was locked and not within sight… they came armed with an angle grinder, so no amount of locks would have helped I don’t think 
I had a hardened steel plate made. I take of the wheels and bolt this on. The nuts are then covered by a steel plate and padlocked. The problem is that if they are committed I do not think that there is much that can be done to stop them.
I have seen a hardened steel bar cut like butter with bolt croppers and as you say an angle grinder just about goes through anything.