More reinforcement or fabric within the concrete would have slowed them down

Lock-on tubes were plastic piping wrapped in chicken wire and rubber, placed in a cardboard mould (lined with heavy gauge plastic and bound with gaffer tape to prevent it disintegrating) before being infilled with concrete. This took two people one day to make (though one person did have a broken arm...). Police were able to cut through concrete and wire with lump hammer and cold chisel, some fabric may have complicated things.