Speeding up a sit

I work on this while working on obedience as well. While doing a walking heal I will blow the whistle (crop behind my back) and tap them on the rear. Some dogs will need a firmer tap. I still do this on occasion but i did it before every workout that required a remote sit. I was having the same problem and this worked for me. As for correction in the field go with the nick on the second whistle as Wayne suggested. Good luck