Police in Shropshire have invested in recently-developed technology to try to stop metal thieves.
Police ultimately hope to protect every building in the borough
SmartWater is being used at vulnerable premises in Telford and Wrekin to help officers track down offenders.
The liquid contains a DNA-style code, which is unique to each location treated with SmartWater and emits a tell-tale glow under ultraviolet light.
The technology has now been installed in schools, colleges and other buildings in the borough.
West Mercia Police have installed ultraviolet lighting in their custody suites.
Anyone who is arrested must walk through the light and if the person has been in contact with SmartWater it will glow brightly.
Telford's Crime Risk Manager, Dave Williams, said the eventual aim was to have every building in the borough protected.
"We are also working closely with local scrap dealers to ensure they understand the SmartWater concept and they will soon all possess their own ultraviolet lights," Mr Williams said.