London has some pretty effective pickpockets (try Covent Garden on a busy weekend in Summer). Prague petty criminals prefer the accidental bumping into you approach, especially in the main tourist area outside Tyn cathedral/Astronomical Clock in the old town square.

I must admit that I relax a little when I enter an academic environment.

I have one of those wallets that have little straps that hook over your belt, and then you put the wallet inside your trousers. Works for me.