If I go to a bike gathering where I have to "lock up my bike" because I don't trust the people at the group gathering......I don't go to that group.
Otherwise, I park it, take the keys out and walk away. If someone takes my bike over everyone elses...well, I guess they needed it more than I did, and I have insurance.
No, really I have a cable lock and I lock the two frames together, along with disk locks, but this is only to slow them down, if they wanted them they would find a way to take them, just keep your insurance paid up.
Aside from the common sense stuff like lock it and take the keys I carry full coverage insurance. If they want it they will take it, I prefer they not destroy it in the process in the rare case it is recovered.