Laws for Adverse Possession in Utah

I live in Morgan county, UT. In April 2011, my neighbor had some very deep concrete curbing put in on a corner of his lot. Upon completion, I noticed it went at least a foot over onto our property. I asked him to fix it a couple of weeks after install. He apologized and assured me that he would fix it. Not only has he not fixed it in over 5 years, he actually tried to sell the house about a year ago knowing about the infringement. I told the real estate agent about it. She saw it for herself and expressed frustration that the owner hadn't disclosed it. The sign was gone the next day and he hasn't tried to sell it since. He's never mentioned the issue again to me since I brought it to his attention in 2011. What do I need to do to protect against adverse possession? Since the key is the infringement is without the owner's permission, can I just send him a certified letter saying the curbing is on our property with our permission? Thank you.