I`ve found a good way to deflect crusades.When I know a crusade is coming I start sending armies to the entry point into my land.When the crusade reaches the province above my land,I attack with a very small army(sometimes just one unit) Of course they lose,but it keeps them from invading,all the while I build units.After a good 8 turns,the crusade doesn`t have near the amount of men it had to begin with,and since I am building units,I have a large army ready to invade