For this type of situation, where a foreign key may point to different tables I use a structure like;

Field Name         Description
TablePK            The PK for this table
OwnerTypeFK        A foreign key to a lookup table of all possible OwnerTypes
                   (ie Employee, Vehicle, or Place)
OwnerFK            The FK value for the specified OwnerType

You also use additional fields in the OwnerType lookup table to store the rules like a what OwnerTypes are legal for each OwnerType.