From Halligan's website:

My sculpture examines our interpretations of boundaries and how we relate to them. Cautionary symbols are combined with three dimensional forms to create physical objects that by their very nature indicate boundaries and warnings that, although ambiguous as to their nature, ask questions of the viewer regarding the nature of place and ones interactions to it. I feel that by being aware of our imposed boundaries, including those self-imposed, and the potential lies that are associated with them we can better understand ourselves and perhaps even approach knowing some truths.
The forms reference Neolithic megaliths that I have encountered in Ireland, Scotland and Cornwall. I see them as both archaic and contemporary forms that visually impact us and pull on our collective consciousness. I make my sculptures out of steel and concrete. These materials I feel are as accessible, for me to use as were the giant stones moved and erected by my Neolithic forbearers.