I worm my sheep with Ivermectin paste and Panacur liquid, alternating quarterly. Still ain't easy, ya gotta catch 'em, but it's better than trying to poke a pill down their throat.

A tip if you use paste/liquid: Sheep got no teeth in back. You can stick your finger in the corner of their mouth without getting bit and slide a syringe (less needle, of course) fulla liquid in there and squirt it right down their throat. Ivermectin paste comes in it's own syringe, you just set the stop for the proper amount and squirt it in.

Ivermectin is primarily a horse wormer, you just use it in much smaller amounts for sheep. Dose by body weight is marked on the dispenser.

This rotation was recommended by my vet.