I'm late to this conversation, but.... as far as going on land that is posted, fenced, etc. ALL LEOs have the authority to be on that land per the USSC. It is called the Open Field Doctrine. Look it up. They can not enter an building or curtilage of that building without a warrant unless there are extenuating circumstances that necessitate entry prior to obtaining a warrant. This is how mary jane fields are found and why GW's can look for corn or baited dove fields.
Lord, please help us get our nation straightened out.