Scratch, mark or ingrave an identifying mark in/on trim panels etc, ultra violet pens are ok but can fade over time, dremel the VIN number on the back of dash boards, switch panels, upper lower steering column covers etc, indelible marker under seats, door panels, stamp your own mark on engine blocks, engrave carb bodies..... use your imagination, take photos and keep them safe.
Disklock are good, stoplocks, crook locks are crap, stock locks can be defeated with a common garage tool with minimal noise.
Remember the old pedal locks back in the 80's? They work.
Sheild where possible the inner door rods and consider making a steel cage around the ignition lock, not every one uses a feeler gauge to wiggle ya lock, usually use a tube slid over the barrel and leaverage to smash the steering lock.
Get an old nokia and hard wire it, hide it up the dash, fit a cheap hands free kit and set the phone to auto answer and silent. Then register the phone on the net and you have a cheap tracker... and if the worse happens you can call it, it will auto answer in quiet mode and you can listen in!
Fit a heavy duty indicator relay with a couple of blocking diodes and a switch to the rear lights, if scrote takes the car and doesnt switch the switch the relay makes the brake lights and reverse lights flash, that might draw attention to the car.......
If I can think of more I will post them, I dont fit car security nor am I a car theif! Just been involved in security since 1991 and did 7 years with londons finest.
Hope that helps and hope I havent bored you all silly.