Who's your baby sin? o_O
On topic - If you're doing like 30k DS on them, then they are basically Double dagger'ing. Trap them, they'll backslide, you arrow shower, and repeat. DS them whenever they're open. I'm not too knowledgeable on the Sniper class, but I know most SinX's don't know how to backslide properly. Also, you should hunt some berries too.