SGS can be scratched too, gorilla glass is like bulletproof glass, put it to enough abuse and it'll still break/scratch...additionally your everyday normal sand is actually quartz or silica, which is like the 4th to 5th hardest material on earth...so unless your screen is diamond its gonna be scratched sooner or later.

there's a number sequence to access that option, but i forgot the combination, try google for it, i remember there you can set the things you mentioned.