4) (from advice someone on these boards gave me) break sea chains so your stretch of ships for trading and transport do not allow a path from the province with crusades going through it and the crusade target. Forces the AI to re-route the crusade.
Notice that crusades can only use the province owner shiplines. So if you're the English and got crusade on your lands, they can only use your shiplines, not even thier own (well we humans can't, that's for certain).

2) lower the zeal of a province by letting one of your own crusades sit in a province for a VERY long time ... when it's depleted send it on a suicide mission to get rid of it. Low zeal means almost none of your troops get recruited.
That will cost you influence though.

I crusade quite often, but mostly only to rise the influence and piety of my king. Unless it's GA ofcourse.