most of the traps will have to well hidden to work. this is a schematic for a test server so you can see how it works.
I hide similar versions of this in jungles and caves(with more dispensers in different configurations(this is just the trigger) .
(mine the diamond to start, this will spit fire in 3 directions)
this is a simple design, you can make it insane with fireballs and arrows going every which way. enjoy