I am new to all this - got a bike as a retirement present and bought a Saris Bones 2 bike rack. It seems to me as it is just clip on it could be stolen while I am happily off riding my bike - is this a serious risk or am I just being paranoid? If it is, any solutions?
The metal brackets that clip on the edges of the trunk lid cannot be removed when the trunk is closed and locked, so no-one is going to casually unclip the rack and walk off with it.
I suppose someone could lever the brackets out, but that would damage the trunk lid and surrounding bodywork, so you would have a bigger problem and an insurance claim.
Also the straps could be cut, but what is the point of stealing a ruined rack?
Nothing is theft proof for a determined thief. The best you can do is make more difficult to steal than a similar item close to yours. If your rack is hitch mounted a small cable looped through the chain eyelet or a hitch pin lock should be sufficient. A trunk mounted rack can be secured in a similar method. Attach a length of cable to a block of wood. String the cable through the rack and place the block of wood in the trunk. The rack cant be removed unless the trunk is opened. You could also remove the rack and store it in the trunk while you are riding.
Taking it off and put it in the boot is the best protection, however if someone is prepared to steal the rack off the boot, they are just as likely to break into the car and help themselves to its contents.
You could add a steel cable requiring bolt cutters to deter the thief but it won't stop them. If the bike rack is harder to steal than just breaking into the car (which is trivially easy for those that don't care about damage) it is as secure as possible. To prevent damage to the car and associated costs, you may be better to let them get the rack.
Make it so nobody would want to steal it. Paint it Pink! And who is going to go walking down the street with a pink bicycle carrier? Not only is that embarrassing, but anyone who can see it would take extra notice of the guy. Because you have got to want to know what guy has a pink bike carrier.
Of course if it was a girl thief then the pink carrier might not be so out of place, but it still will get noticed. (although I think the likelihood of a girl bike carrier thief is a lot lower than a guy)