Some of my cameras have the holes where a cable lock can be threaded through in order to lock it to the tree. The problem is that most cable locks do not fit through the hole.
One solution I have found to this is taking the gun locks that you might get with a new handgun purchase, similar to this:
I run this through the holes on the camera and then run the cable lock or log chain through the gun lock.
This is a clear case of smoke'um if ya got'um. Purchasing the extra lock may be cost prohibitive in some cases, but if you already have a lock laying around it does the job. I am sure a good set of bolt cutters would make short work of this setup, but i'm of the opinion that you will not stop a properly motivated thief.