A method for applying a barrier to structures to prevent the infiltration of pest species (unwanted organisms) uses a (e.g., coating) composition formed from a polyurethane (e.g., film-forming) polymer system and a pellet comprising a pesticide incorporated into a sorbent and dispersed in the polyurethane polymer system. The composition protects the structure by application either to the structure or to a pathway that leads to the structure. Advantageous polymer systems include polyurethanes rich in urea linkages and predominating in aliphatic and alicyclic backbones.