Always ensure safety is the top priority for you, your family and employees, and the protestors themselves. An accident or injury of any kind could cause significant legal problems and be used to justify activist campaigns.
If your farm is protested without warning, call the police and express your concern for your safety and the safety of your family. Be very clear you are not sure of the intent of the protest and you are fearful.
Be very clear when initially speaking to the protestors, advise them they are not welcome, if they enter your premises they will be trespassing, and that you have called the police. Ask them to not enter your barn or buildings. Do not engage with the protestors beyond that statement.