Peppercorn in vent to find hidden nest?

I have 3 chickens who I allow free range over a 4 acre fallow field. Unfortunately they have gotten in the habit of creating their own nests, though I do provide elevated nesting boxes in the coop with bedding.

I googled (probably not a good idea to trust google but any-who) and found a page advising placing a peppercorn in the chickens vent, tricking the chicken into thinking it needs to lay. I had some misgivings but unscrewed the pepper shaker and went fiddling with tail feathers.

And? Nothing, I mean the girls were unimpressed with being flipped upside down and having me probe them with my finger but once I had let them down they just stood their waiting for me to feed them.

Had this worked for anyone else? Did I do something wrong? Will I find the peppercorns ensconced in the shells of my hidden eggs?

Have you any suggestions for how to possibly find the hidden nest? I am afraid of attracting predators.