the gps isn't a bad idea...cut out a small area in the bottom of the seat foam towards the back of the seat where you won't be putting much pressure on it while you're out riding...and tuck it in between the seat pan and foam...no one would ever know it's there.
I keep my bikes in my living room with multiple 1/2" shank locks through the front rotors and rear sprockets...my place is alarmed and has 8 cameras...4 that watch the house, and 4 that watch the property, and my dog is always inside when I'm not home...and most people in my area know that my family is all in law enforcement. If a thief wants one of my bikes, they'll have their work cut out for them.