drill a small hole in the intake just below the water line, that way if if
starts to leak out of the canister it can only leak to the level where the
hole is at which time it will start sucking air and the siphon effect will
stop.

Thanks,
I'd forgotten to do this on my latest filter.

I do mine about three inches below normal water level so I don't have to
re-prime after routine water changes but the tank won't empty too far.

( I do have ceramic floors though - waxed wood or carpet would make a
spillage a bigger issue ;o)