Spiderke,
I do not think that a GPS device will be much help - my sense is that that will just get "lost" with the laptop before you can start the tracking process.
Think about the circumstances that caused the previous three losses.
Is theft the issue or are you just forgetting the laptop when you leave somewhere?
In any case you may do better with just a low tech lockable tether cable. One end on the laptop and the other end to your book bag/backpack. Or even yourself if you tend to set the laptop aside somewhere, doze off, and leave it.
And certainly put the laptop out of easy sight and reach whenever you are not using it.
And, just for good measure, at least put a phone number/reward offer card on it. There are still a...