We went through a few bycicle
cables, but the problem with them was that once the
water got under the plastic, the cable started to rust. Fast.
Now we have a solution similar to the one suggested by msponer, but we got an already made 15' thick cable inside a rope made by Ronstan from Defender (can't find it on their website now...). It's worked for us for the last 3 years and is still fine.
Regarding having a not very noticeable
dinghy - sometimes people just take dinghies at the end of the night after the bars close to get to their boats. We've seen people ending up without their dinghies just for one night, but it's still not pleasant to not be able to get to your boat without swimming at 3 or 4 am...
For the
engine we know of two options:
1. Just use a padlock that you fasten through the holes on the screws that hold your
engine to the transom. Make sure that the padlock is
water and rust proof. We use Masterlock. Even so, spray WD-40 into it generously every month.
2. Buy a bar that slides over the engine to transom screws and lock that. Apply WD-40 to the lock (that is of course rust proof).
But remember, people who are really after your engine or dinghy, will do so in any case. We saw a dinghy in
Nassau with a hole at the top of the transom. People just took a part of the transom together with the engine.