Simply offer a few dollars
The current law is quoted below from the Illinois DNR Website.
Attention Landowners: A landowner is NOT liable for injuries to anglers, hunters, trappers, campers, snowmobilers, motorcyclists or other recreational users who use this land IF a fee is NOT charged and IF the injuries were not caused by the gross negligence or willful misconduct of the landowner.
(The "Recreational Use of Land and Water Areas Act" 745 ILCS 6511-7)