I'm not sure how common it is as I have only visited a handful of slopes, but some places offer ski valet service. The hill I most often go to has one beside both of their "chalet" bases. It nominally costs a couple dollars, but it's free for people staying at the resort, and the guys have an unspoken rule to assume you are staying at the resort and not charge you anything
. My setup was bought used, it's not expensive and quite beat looking, but I still give it to them for safe keeping.
At my local resort I would probably just keep it unlocked if I did not have the valet option, but if I went somewhere else for a snowboarding trip, I would probably lock it because if stolen, I would have to either pay through the nose to replace it (wouldn't expect very low prices right next to the lift), or calling it quits until I can obtain a reasonably priced setup.