use ivomec mate ,0.3 ml for a terrier you can buy it from any farm supplies just say its for cattle when asked ,benzyl benzonate dosnt work that well on mange and the dog might get worse ,ivomec kills just about everything in the dogs body including round worm, heart worm, lung worm mites and anything else lurking ,if you got other dogs to give them a jab if you got any lurchers with collie in them then i wouldnt do them as collies cant deal with the stuff and is said to be fatal ,i do my terriers all the time with it and a bottle costs about £25 and will last the dogs life .