Wire or cable-tie noose so if they try again you can snare them and stop them from running away, then free them at your leisure under your own terms and suitable punishment so they won't try it again
I like your ingenuity though with the tacks.
How about something else on the inner wall top (where those nails are) to prevent someone reaching right over?
Barbed wire all along that wall line with warning signs to cover yourself? Signs will stop you getting sued.