If your motor is attached to your transom and not on a bracket you can get a special ss bolt and nut (drill thru transome) that requires a special tool to loosen it (like expensive auto wheels) and bolt the motor to the transom... Very secure -- West Marine carries it..
Put it on my son's gregor w/ Yamaha.

I use the bar shown in picture over clamp handles --but I understand that if the motor is twisted sideways pulling on shaft they can be pried off.. ( I almost wish they'd steal my 6 hp '73' Johnson!!)

Well last month someone got into my canopy in my driveway,,dog barked briefly 3 am, I didn't hear and wife ignored --the creeps took a brand new unused Minn Kota 65# motor, Shindaiwa hedge trimmer, tool box etc...

So now dog barks,,,,,I grab 38,, put on slippers and rush outside (3 times since then 3-5 am) Nothing,,,,,not even a possum!!!!

I have designed a booby trap device w/ shot gun shell ignited by a firing pin released when someone door - it will be hand loaded w/ paint pellets, pepper or something not deadly but will wake the neighbors and scare the pee out of cruds!!!! Need to get a deputy over to check it out and get his opinion.....So what do you guys think??????