Once a pup knows the 6 send drill I go to KRD's. I like to do ~60% of my KRD's as a mark then pick up the blinds and ~40% of them as poison bird blinds. I do 2 or 3 a week during the off season as I can do them without a big group. I throw in an interupted marking setup maybe once a week during the heavy training season.
I learned the 6 send drill from Woody Thurman when he came up here and did a retriever training seminar in 1992. I've done it with every retriever I've had that made it through the double T.
Basically, you set out 6 bumpers in a pile I do it anywhere between 100 and 150 yards. Get the dog and run a blind to the pile. Next run the pile again. The dog should line it or be better than the first time. Next put a gunner out there two thirds of the way to the blind. Just have the gunner sit there and run the blind again. Next, have the gunner stand up and fire a dry shot, run the blind. Next have the gunner fire a shot and throw a bumper/bird. Pick up the mark and run the blind. Last have the gunner throw a mark. Run the blind then pick up the mark.
The first few times you run it you're teaching it. After half a dozen times the dog usually has a good idea of this and I start doing only 2-3 a week for a couple/three weeks. At first run the mark 90 degrees off to the side but slowly work closer to the line to the blind. At the end your running mark very close to the line to the blind,don't forget to do some under the arc blinds. I do it maybe 12-15 times and then I don't come back to it. After a few of them you are only doing a 4 send drill and later on maybe only 3 sends.