If Arthur was hiding within the perimeter of Cayenne's property like his two idiot men, the secret guards would have found him. Stefan thought he outwitted this person but the intelligence of an honor student can't be underestimated.
Arthur investigated the other owners of the neighboring properties around Cayenne's place. He befriended them, feeding them nonsense like his wife was cheating and was living in the nearby property. He wanted to catch them red-handed and thus; the owner of the neighboring property allowed Arthur to come and observe Cayenne and Stefan from afar.
"I have seen them for a while now. It's been over a month since someone live in this place and the guy just came over after two weeks that your wife moved there." the old man who owned the property told Arthur. He was also the one who lent Arthur a telescope.
