You may think this sounds funny but i know of someone that keeps a couple of geese in his garden along with the fowl and if anyone or anything enters they kick up an awful racket,b*****ds would deafen you,better than any alarm.
Guinea Fowl are great for this too, Jesus the racket they make if any unfamiliar folk are about!
how would the gleanies be on open grass or are they better in woodland? just a thought as i may be getting a small bit of extra land to free range a few hens on ,were about most of the time and when were are the dogs are about but something a bit vocal is alway