So you're talking about overvoltage on the output of a regulator, not an input?
The appropriate solution depends on knowing the origin of the overvoltage. If it's due to some kind of transient overshoot on the supply regulator, then modifying its control loop is an easy solution. Methods like crowbars should only be considered only when absolutely necessary, since their operation usually protects certain parts of the circuit while shifting the hazard to other parts. For example a crowbar might prevent a supply voltage overshoot, but in the process of clamping the supply voltage it may destroy the regulator for the supply, unless you use some sort of fuse.