Is there a contract trick whereby pilots can't leave??
Funny you should mention that! Here is an example that has happened in FR:
Imagine getting a job elsewhere. Your hand your notice in. You were bonded for a type rating when you joined as a Direct entry Captain. You served the bond time, though and you give the required three months notice. Long story short, Ryanair says there is a typing error in your contract and the bond was for a longer period then you thought. We are taking your last two months salary, we want the balance of the bond money, our legal fees, and because you are leaving before the end of the bond we have to hire a contractor to cover your flights and the minimum period we can hire him for is 6 months, so you have to pay us his salary for that period too. And our legal fees (As it usually gets to that stage when it goes that far). Most non Union protected Pilots have to cough up the cash for the sake of a quiet life.