They should be working on the SEP field. Hitchikers guide reference: "The technology required to actually make something invisible is so complex and unreliable that it isn't worth the bother. The Somebody Else's Problem field is much simpler and more effective, and can be run for over a hundred years on a single torch battery. This is because it relies on people's natural predisposition not to see anything they don't want to, weren't expecting, or can't explain."