You question is really asking about a bunch of different failure scenarios and without more detail (really, more specification) it is difficult to answer in any detail:
Too much voltage (temporarily)
You need a "transient voltage suppressor". They come in many forms and scales from large consumer products to build-your-own with two diodes.
Too much voltage (constantly)
You need to reduce the voltage. There are basically two categories of solutions "regulation" and "drop/unregulated".
Regulators are available in everything from commercial switch-mode power supplies to individual IC's.
Unregulated voltage drop can be achieved with just a properly biased diode, a resistor, a step-down transformer, and many other approaches
Too much current (temporarily)
Current is a bit trickier since it is controlled by the load (and anything shorting it). Fuses and other energy threshold based devices will be too slow to react in the general case.
You will probably need to "slow" the current transient down (reduce edge-rate), by applying inductance in series, to buy time for whatever protective devices you employ to activate.
Current transience is best handled by active devices (sense-and-respond) -- just my opinion -- since you usually have a rather complex set of criteria to distinguish between the "good" and "bad" cases.
Too much current (constantly)
HELLO FUSES!!! =)