Wis. Stat. § 90.03: Partition fences; when required.

The respective occupants of adjoining lands used and occupied for farming or grazing purposes, and the respective owners of adjoining lands when the lands of one of such owners is used and occupied for farming or grazing purposes, shall keep and maintain partition fences between their own and the adjoining premises in equal shares so long as either party continues to so occupy the lands, except that the occupants of the lands may agree to the use of markers instead of fences, and such fences shall be kept in good repair throughout the year unless the occupants of the lands on both sides otherwise mutually agree.