Arduino and Servo Motor Control Answered

I was wondering if I could control higher voltage servos (lets say off a 18v battery, more than my arduino board can handle) by building a separate circuit for my servos power and ground wires and putting my servo's Input/output (or pulse if you prefer) wire directly into the arduino board's sockets.  Would this a) damage my arduino? and/or b) effectively regulate servo positioning? (fritzing file attached).   Or would I be forced to use relays?        Thanks, Authority28