Cable locks are useless, they can be cut with a set of side cutters. Nor will any old chain work, no matter how heavy, against bolt cutters. Hardened dedicated bike chains are very resistant to even large bolt cutters but are very heavy and expensive.
If a tree is handy we lock our trikes up around a tree with Kryptonite's best chains and locks. We can also use one of our RVs leveling jack legs to lock to. We also use cable locks that alarm when the cable is cut. On top of that we have motion sensors that alarm if the trikes are moved.