I was fasting, praying for a person who was not and could not be near me. I was unlikely to hear from them whether my casting out prayers had worked. What's a minister to do then?
Ask G-d for a monitoring spirit to enter an object or animal near you.
I remember once praying against a Nazi stronghold on a Germanic descendant who was not near me. As I did, my dog who was near me started trembling uncontrollably. I knew the work was done.
After this I prayed them out of other demonic oppression and went on to ask Holy Spirit to dwell in them to the fullest and to seal them in Messiah. I went on to pray for no spirit of retaliation.
This, in my experience, is harder to do if someone is under satanic oppression from being in a cult like Mormonism or paganism; or in a demon-based religion like Buddhism or Hinduism. But if the person was once a Christian, it usually works.
Monitoring spirits. They are useful angelic presences. I thank them and tell them they are free to leave as the work is done.