Hello, I have some questions about different vibrato or tremolo system

In a thread about the Bigsby style vibrato, and someone said that the strings will pop off if you pull back (push down? can't remember) to far, but the strings are on pegs, right? So could you have some sort of locking system to keep the strings on?

Is there some sort of two-way tremolo or vibrato system where you can de-tune without having to adjust springs or anything?

and lastly what are some different tremolo or vibrato systems? I only know a few.

Thanks, Adam
Washburn A20V 1981
Stagg SG300
Ibanez Iceman
Jackson King V
Epiphone Special II
Epiphone Embassy IV
Martin D-16RGT
Ibanez EW20WNE
Not likely. The Ibanez ZPS will help if you drop tune or break a string though.