Thieves planning to steal lead from church roofs may get more than they bargained for - a jet of hi-tech liquid laced with particles that are impossible to get off.
Leicestershire police are to set up devices that hose out Smartwater at those who are targeting churches after the price of scrap lead skyrocketed last year.
The low-pressure spray can be triggered by a motion detector, pressure pad, or a "panic button".
The solution, visible only under ultra-violet light, contains microscopic particles encoded with a unique number to identify where criminals were sprayed.
Manufacturers say the solution takes about 12 weeks to come off skin, and cannot be cleaned out of clothing.
Thieves can strip churches of Å50,000 of lead in a night.
Wardens have been painting Smartwater on roofs for several months, but the spray "trap" is a new idea.
Church wardens saw the new technology at the police headquarters, in Enderby, last week.
Officers want to keep the location of the spray traps secret so criminals are caught by surprise.
Lead thieves have attacked the church of St Peter and St Paul, in Syston, three times in the past three months, causing more than Å70,000 of damage.
Warden Brian Middleton said: "I think the spray is a good idea. The only thing I can think of is if they do get sprayed they could just get rid of the clothes, but if it gets their skin it won't come off for weeks.
"The stuff is good because it can be painted on to the edges of lead and if it is found at the scrap yard later, police can sort it out from there.
"We've had three hits, two on the north aisle, and a small hit on the parapets on the other side of the church.
"They are going to cost Å70,000 to replace it with lead, and Å50,000 if we use stainless steel.
"We've been given Å15,000 from the insurers, which means we have to find the rest from church funds."
Pc Stephen Day, the south area's crime prevention officer, said: "The purpose of the meeting was to discuss security with church wardens.
"It can be anything from making sure people lock up at night to Å3,000 CCTV systems, and anything in between.
"It's often thought security can be ugly, but things like wrought iron gates with the name of the church in them can really help.
"We've used the Smartwater spray devices in other operations, for instance "honey-trap" cars, but this is the first time we are using it for churches."
Some churches have been turned to CCTV to deter thieves.
Six Braunstone churches installed rooftop CCTV cameras 15 months ago with cash from the Braunstone Community Association.
A spokesman for Smartwater Ltd said: "Police are now routinely scanning people with UV lights when they are brought in.
"So they could be brought in for drink-driving and be identified as a lead thief weeks after they were on the roof."