Yep, accidentally dropped it off a bridge.........................
I don't think that will work. Police divers will search the river bottom. If they find it, chances are they'll be able to recover the data, unless it's been physically damaged.
If it's physically damaged, they'll be able to figure out how. Tool mark analysis is quite advanced, with EDAX, NAA, and SEM technology.
If they don't find it, they'll want to know where it really is.