I have a small cart like Catrionas that usually comes along in the car. If I have to carry my kayak much more than 50 metres or so my back starts to protest, not so much from the weight but from trying to stabilize 5 feet of swinging weight. Mine tends to fall off too if the ground is too rocky, but for flattish stretches it's great, I've pulled my kayak over 1 km on it. I usually hide it or just leave it visible since it's not valuable, but you could just bring a small bicycle lock too and lock it to a tree or something. I figure it's most likely to be taken by a kid on a whim, or by someone who doesn't realize it's left behind on purpose.