Once we progressed beyond the plastic containers, we hit a bit of a road block with the cardboard box. First I kept the sides too high and the dogs were having a more difficult time balancing and figuring out how to maneuver each foot over tall sides. Once I cut the sides of the boxes down, things moved along a lot quicker.
Then I had a problem with the bottom of the boxes being too slick. The front were fine pressed up against the front of the box, but the back feet would slide as they were getting placed. This led to more cautious dogs who weren't really thrilled about trying to balance on a relatively slick surface. I tried spraying the bottom of the box with water, but that just got absorbed and we were back to the same low traction. I tried adding hair spray to the bottom to make it sticky, but that didn't really work either. The one trick that I found worked really well was coating the bottoms with duct tape. And we just happened to have some neon orange duct tape "lying around." :) Once there was traction, the dogs were happy.
Bess impressed me the most with her little box that she was able to balance in. Heffner's feet just wouldn't all fit in there and I wasn't about to even try it. I continued to work with him in his smallest box, while I continued to work with Bess.
I was also impressed with how Bess went from being very cautious about offering anything to happily hopping in and out of the box and being willing to actually try offering things. I should make a video of that alone. If you could see the entirety of her very first video compared with her last one, it was a HUGE difference.