[Carl n Susan]

I use a cable lock like this:

Mine is a bit longer which allows me to wrap it around the power pole and take advantage of any fixture which help keeps it from being removed. That said, most of my camping buddies don't lock down their portable EMS devices. We never have had a problem in over 10 years of camping in lots of private or public parks. I do believe just the presence of a cable lock deters the casual thief. The determined one will get it regardless of what you do.