Is there a way to prevent Lords from escaping?

You may only take prisoner people you have knocked unconcious. You must first take down the Lord, then take down their armies. However, if you take a Lord prisoner he may escape after some time traveling.

Escaping: For every 72 hours the Lord is in your party he has a 50% chance of escaping. If you have a jail in your town, you can put him in their and he only has a 10% chance of escaping

Source:
http://mountandblade.wikia.com/wiki/Prisoners