A pdf of the guidelines can be found here (10kb).

Metal Detecting Guidelines
Wausau & Marathon County Parks, Recreation, and Forestry Department
1.  State and county regulations prohibit the disturbance or damage of natural features and entering closed areas, therefore some lands may not be open to metal detecting.
2.  Metal detecting is not allowed in environmentally sensitive areas and archaeological or historical sites.  The Federal Antiquities Act prohibits the disturbance or removal of items of cultural or historical significance on public lands.
3.  Presently a permit is not required; the Department however expects that anyone participating in this activity will follow the “without a trace” philosophy.
4.  Shallow ground probing within the top six inches is permitted, however removing soil to locate something that is buried, cutting back sod or digging holes is prohibited.
5.  Caution must also be exercised because some park and forest properties have buried utilities.
6.  Metal detecting is prohibited at large public events or near shelters that have been reserved for private events.