[quote=@Savato]
They do seem to have some pretty insane defenses. Do they need a special weapon to die or some super hard hits like Eto karate chopping them would work? 
[/quote]

Well, besides sufficiently big explosives (I believe they hit one with an airstrike from a drone to kill it), the SGC was able to develop a device that disrupted the energy keeping them alive, since the Kull had short lives, resulting in them dying while bypassing the energy absorbing armor that they wore. 

Of course, that's just the Mk 1 Kull. Ba'al has made some....improvements, since he took over the Goa'uld Empire.