Apologies in advance because this is going to be long! You made me really think about all the little things that we did to put the behavior together.
I forgot to ask, How did you go about training the 2o 2o method & how long did it take her to understand fully ? 
I think Tara's understanding of 2on/2off really stems from our foundation work. Formally, I used the target method to teach the whole behavior. From the beginning here is what we did...
In our very first “pet” obedience class (before I even knew we were going to do agility!), I shaped a hand target and transferred that to a plastic lid. I proofed the target on the plastic lid by holding it in my hand in various positions, attaching it to vertical surfaces (walls, cabinets), putting it on a chair. I'd say she understood this behavior pretty well by the end of that first class, but I didn't use the lid much at all for several months and stuck to hand targeting only. When we got to our first six week foundation agility class (in May of this year), we started practicing targeting with the plastic lid again. We started with just a regular targeting action, and worked up to targeting on the floor VERY slowly. The first week, we just held the target in our hand below the dogs' heads, the next week slightly lower, and slightly lower than that till we had the back of our hand resting on the ground with the target lid in our palm. After several weeks, we were able to fade the hand, but leave the target lid. It was important at this point to make sure the dogs did not lie down or offer a foot target.
Prior to our first agility class, I had also been working perch work with Tara. I shaped the perch with her front feet on at first and then decided to do with her back feet on to increase her rear end awareness. We did more of this than was probably necessary and as a result Tara LOVES to perch. If she sees anything even remotely resembling a perch (I had used a huge science textbook), she will start offering behaviors putting her front feet or back feet on it. She even perched on a can of tuna once. :silly: I never put this on a cue as it was just something we were playing around with, but I think it was really important to her understanding of the 2on/2off position.
Back to our first agility class and we were doing “board” work also, teaching the dogs to stand with their back feet on the end of a 4-6 foot long board and click/treat for staying in position while moving around it. Basically, teaching it as any control/stay position. There was TONS of reinforcement in this position. So much actually that I had to start reinforcing the release from the position also.
Our next class started and we started to put the two pieces together – target + rear feet perch. When she would offer her rear feet on the board, I would place the target on the floor in front of her and let her offer the target also and mark/treat. The treat was always placed on the target or from my hand right at the target to reinforce that head down position. Once she started getting this, I made it harder by walking from the end of the board with her to the target (from both sides). We practiced this at home on a board and in class while waiting our turn for other obstacles. It took awhile (a few weeks?) to really understand that both the nose touch to the target AND the back feet perching on the board had to be present for her to get it right. That's probably mostly my fault for clicking by accident a lot when I didn't notice that she had one foot off the board. By the end of this class, we started backchaining the A-frame and dogwalk, starting with the 2on/2off position. This was also when I was happy enough with the behavior to name it “target”, up till this point it was purely shaping and Tara was offering the behavior only. We also started fading the target by cutting the lid down about ½ inch every week or so.
We had about a 3 week break in between our second agility class and our current one, and I managed to fade the target to about a dime-sized piece of plastic. The first night of our current class, we discovered she didn't need it anymore when she was bobbing her head like a chicken at the ground despite the fact that our teeny target had gotten pushed out of the way, and we haven't needed the target since. We did our first full length run of the A-frame and the dogwalk at the 2nd class (I think) and she has been brilliant at it.
Right now, the only time she fails on her contacts are when we add a new element. For example, in the video she blows past the contact on the dogwalk the first time because she had a lot more speed than she's ever done it before. She learns from her mistakes very well though and rarely makes the same one twice in a row.
So, I guess we've been “formally” training the 2on/2off for about 4 months. I think she understood the position fully by the end of 2 months, but I do not think it's fully proofed yet under all circumstances. I still need to proof a send to the target, recall to the position and moving laterally away from her while she's driving to the target.
