Re: cut-proof cable for securing dinghy and motor?
rm, cable and chain are as good as it gets. You can buy a "motorcycle" cable in the big hardware stores, with the end keyed up so one end plugs into the other and a key locks it. Use WD40 regularly or something similar in the lock and it lasts very much longer. Or buy some chain, or have loops swaged on a heavy cable, all comes out about the same in terms of protection.
The thing about a substantial cable or chain, is that is slows a thief down and requires them to carry tools, and carrying "burglarly tools" in itself is grounds for arrest in many places. Not to mention, passerby tend to see or hear that stuff.
If you can make the engine or dink look more like a beater, that's even better. Desecrate the engine cover with rust primer, make it look old and abused and patched. Do something to the dink, like gluing on contrasting color panels, that make it easier to spot and harder to resell.
I think the best advice I've heard is to install a waterproof inspection plate near the waterline, and take it with you when you leave. Someone gets in the boat, their feet get wet, they try to move it and more water comes in...All you can do is try to make your target less attractive than the next one.