POLICE have stepped up their battle to weed out triads who have infiltrated decorating businesses working in public housing estates. ''We check contractors and sub-contractors in order to eliminate triad involvement,'' Acting Superintendent Li King-sui said at yesterday's opening of a new police station in Ma On Shan. ''At the same time, we are also increasing patrols in newly-completed housing estates.'' Ms Li, the Ma On Shan divisional commander, said triad involvement in the decoration of public housing estates could be happening in every new town. In some cases, residents who refused offers by suspected triads were assaulted or threatened. Legitimate contractors might also be victims of intimidation by triads, she said. The Housing Department manager for New Territories East, Mr Kwok Chi-tong, said estate officers were working closely with police to stamp out the problem. All employees of contractors and sub-contractors had been checked by police, he said. The police had also introduced talks and the distribution of leaflets on new estates to encourage residents to report crimes. Ma On Shan police station will house the New Territories South Regional Police Headquarters.