Chewing gum. Yes, I know it sounds ridiculous, but strangely enough it works great.
How do I know? Many years ago, I took a trip to Australia for 3 months. While I was there, I found a little ceramic frog, and just for fun, stuck it to the front of the hood on my girlfriend's mom's car using some chewing gum I had been chewing on.
.. it's STILL stuck to the car, and shows no signs of even coming loose.
Just a thought.