Thresholds? Defiance?

I had planned to walk Tug to the end of the pasture and let him circle on the hill to maybe help his back. I stayed on his right side on the way down to also help with his left sidedness. But, before we got very far down, he noticed a herd of deer in the woods. They were pretty close, and I wished I had grabbed my camera, but none of them seemed to noticed me except one that kept starring at me. I tried to stay out of view by keeping to Tug's side, but I think they heard my radio and trotted farther through the woods. So again, I walked beside Tug and we made it all the way down to the hill when they ran and jumped the fence. 15-20 of them! Tug did really good the whole time. They never seemed to spook him. If he hesitated going forward, I retreated with him or paused and tried again. When I asked him to circle, he trotted going downhill. He was reluctant to stop when I asked, but did when he had to go uphill. Then he acted like the deer were right over the fence in the bushes. I knew they weren't, but I respected his thoughts and tried to help him get over them. I tried the falling leaf pattern - he wouldn't keep moving - I tried sideways and backwards - he still looked to the fence. He just seemed to be getting more spooked, so I moved farther away from the hill and the fence. I tried different spots and finally found one that he was more comfortable circling in. He did pull as hard, and even seemed to come in closer. After some time, I tried driving him towards the hill from zone 3. He'd start off good, but he seemed to stop in the same area. I wasn't going to push him over the cliff if that was the reason, but I also wasn't sure if he was just saying "No." I finally marked the area and he stopped again in it. So I just took him back up the pasture and half way did some stick to me. Then I tried the "patience pole" thing and tied him to a tree. After a while, I went to him, took the halter off and went over to a barrel. He came over and stayed a while.