Introducing saddle

[Jimr]

Hi. I need help. I recently (1month ago) bought 2, four yr old alpine twins. I have spent a lot of time with them hiking around our house and they are doing great. I started them on saddles last weekend, had them tied and put them on with no issues. Yesterday I hauled them (I have two other 2.5 yr olds as well) out from the house to hike and saddled them all, I did the shy 4yr old last. He did fine, but when I un hooked him, he took off, he ran a few hot laps then just took off. I went after him,but he was ahead and got in a fence. Nothing to bad, but some burns on his front leg.  He would not move with the saddle on after that, so I took it off and we hiked just a little and I let them eat bitter brush.  Today I tried again, I have a lot of space at home,so I tried it here. Same thing except I had him on a lead. He does not want to move but he will take a few steps, but then he tries to take off. He did this 3-4 times. He will stand still with no issues. I even took the butt strap off? But moving is trouble. There are no burs on the saddle or pad. So I am wondering how to work him through this. The only thing I wonder about is that he got a vaccine right before I got him and the bump is still sensitive. The belly strap is close to that? Any thoughts? Thanks for your help. Jim