If you can't, or don't want to move the cab all the time, perhaps going into the jack plate and taking soldering clips onto leads for the speakers, and then you could just unplug the speakers from the jacks, maybe even take the jack plate with you or something. Take the fuse out of your head, or just bring it home. I suppose those would be the simplest solutions to the "people playing your stuff without your permission" problem. More complex, would be getting some cheap MCM drivers and stuffing it into an MDF box (maybe with some extra conrete on the bottom for good measure), without wheels, nobody's running off with that thing any time soon, and for less than a hundred bucks you could fit out a halfway to decent cab for practice and not worry about replacement speakers. Then somehow get everybody to sign a conract to agree to pay a small monthly fee to use your bass gear, or at least a contract that would compel EVRYONE else to pay for broken equipment if the need arises, provided that nobody fesses up to it. I don't know how it works in your neck of the woods, but Tort law should be able to compel them to pay.
Also, I've been on the other side of your current predicament. A guy let me use his bass cabinet in a practice space that was in his house, that my band's vocalist was also living in. I'd use his bass gear, he'd use our drummer's kit sometimes, guitarists used their own amps, and we all used the PA. It all went fine until he may or may not have broken our drummer's bass drum pedal (along with some inter-personal drama between our vocalist and him, from living together), so he stopped allowing us to use bits of gear that were his, without notice. To be honest, I didn't fault him much for anything, now I've just learned from experience.
Also, I've been on the other side of your current predicament. A guy let me use his bass cabinet in a practice space that was in his house, that my band's vocalist was also living in. I'd use his bass gear, he'd use our drummer's kit sometimes, guitarists used their own amps, and we all used the PA. It all went fine until he may or may not have broken our drummer's bass drum pedal (along with some inter-personal drama between our vocalist and him, from living together), so he stopped allowing us to use bits of gear that were his, without notice. To be honest, I didn't fault him much for anything, now I've just learned from experience.
