I found some information that vaguely references stallions in Wisconsin on an article about Fences in Agricultural Areas. No specifics on type of fencing, but just in good repair and can keep the animal from becoming loose. It seems as if once an animal is loose there is not much in favor of the owner regardless of fencing or handling technique.
An owner who does not maintain a partition fence in good repair cannot claim damages when the neighbor’s animals trespass. However, construction of a fence does not relieve the owner of swine, horses, sheep or goats from liability for damages they commit upon the enclosed premises of a neighbor. [Secs. 90.04 and 172.01] In addition, under sec. 172.01, some animals are considered so powerful or difficult to contain that the state has imposed liability on their owners regardless of whether the animals escape was the owner’s or keeper’s fault. This strict liability applies to stallions over one year old, bulls over 6 months old, and to boars, rams and billy goats over 4 months old.
As far as the stud goes, I just got off the phone with the owners. There was confusion with an email I sent and they called to clarify. Many people have tried to buy this stud over the years, and my account recently linked with my youtube account and changed my name, so they wanted to make sure I was inquiring and not someone else. As far as leasing him this spring, the wheels are certainly turning. Apparently they were not who posted the ad listing him for sale, so he is not for sale. They truly love this horse dearly, and at this point do not wish to sell him, but are more than happy to lease him over the spring/summer. They also said that two days ago, if I heard correctly, one of their mares just had another of his foals. (I, personally, am not a fan of any form of communication that isn't face to face, so I did not ask questions I have been meaning to ask.)