The guy that owns Stapleford also has a stud farm on the airfield, so it's not unusual to see horses in the paddocks and fields round about. They don't seem to take much notice of the comings and goings.
I can even remember being about to start up when a very young foal which had managed to slip under the fence can tottering up to have a look at what was going on - had to call up on the radio to have him escorted back to his mum!
Maybe the polo ponies are a bit like the characters that ride them - highly strung and lacking in brain cells. Good luck with your efforts to thwart this character.
RD