Like many say on this post, if a thief wants your bike he'll get it. I find the best solution when the rack is down with the bikes on is to reverse it right up to a wall or tree until its touching
View attachment 62337so that it becomes almost impossible to get the bikes or the rack as the scum have such limited room to work - this does not negate the need for additional security such as a tungsten wire cable that can be looped thru' the rear towing eye under the bumper and thru' the bikes frames (and wheels) and around the rack itself (you need a longish cable - around 2.5-3m is what I have). Photo just shows it securing the rack in the unused position. Sometimes fate lends a hand - a colleague at work caught a scum trying to steal his 2 bikes from his bike rack (on a car not a Cali) and the scum was despatched to hospital with an apparent broken arm and some 'unpleasant' facial injuries. So there is a god!