DUTY OWED TO DISCOVERED TRESPASSER
If landowner or occupier knows of a trespasser, there is a duty to exercise ordinary care to warn the trespasser of, or to make safe, artificial conditions known to the landowner that involve a risk of death or serious bodily harm and that the trespasser is unlikely to discover. No duty is owed for natural conditions or less dangerous artificial conditions.
A trespasser is discoverd if the the owner notices them, but also if the owner/occupier is notified by information sufficient for a reasonable person to conclude that someone is on the property.
Anticipated trespassers are treated the same as discovered trespassers, ie, someone who continually crosses over the land.