Do you have a blanket hog in your life? I know I do! My wife has been a habitual cover thief for as long as I can remember. I usually don't mind too much unless it's really cold, and then it's more or less imperative that I keep as many covers on my side of the bed as possible. The following are the top three ways to prevent your covers from being stolen at night.
1.) Cover Clamp
The Cover Clamp system is really the only way to effectively secure your covers at night without resorting to getting separate blankets (number 2 on my list). I, personally, use Cover Clamp every night. I especially like it because I toss and turn a lot at night, and this keeps my covers in the same place. My wife can tug all she wants now, but the covers stay right where they should be.
2.) Getting separate blankets
My wife and I tried this method for a while. It does work but it does have drawbacks. You really only have an extra comforter, so you still have your sheets stolen, unless you actually get a separate set of sheets as well. Also, it's kind of a mess. Making the bed is not really possible unless you remove the extra blankets. I actually tried a sleeping bag for some time. It gets the job done, but I'm not sure it was worth the hassle.
3.) Buying extremely large blankets and sheets
Other than the rather extreme step of actually sleeping in separate beds, this method is a last resort. The problem is that it can be difficult to find sheets and blankets big enough to actually make a difference, especially if you have a king size bed. Also, the cost my be prohibitive.
I hope this list helps some of you. I know it can be frustrating looking for a solution to this problem.