Why do people have to make things so hard gee wiz.
Any dumb kid whos messed with their car stereo knows how to get around a volume nob on a remote amplifier. Install a compressor limiter behind a security face plate AND install an inline fuse for the speakers. you could also measure the resistance of your volume setting and replace the volume control with a resistor. Please don’t give me any of that oh it will hurt the delicate balance of the sound, out door speakers will never be that good. If the kids need the base all that bad, sell them a sunfire sub in a garden rock kit, that will wake up the folks next door.

Enjoy