My 23 year old pony has a Sarcoid on his Sheath. I have tried many fly repellents and ones from my Vets with no luck in keeping the flys off the Sarcoid. A local farmer suggest I try Stockholm Tar with natural antibacterial action. I applied the Stockholm Tar to my pony's sheath the flys immediately kept off , the swelling of his sheath went down and the Sarcoid has reduced in size . I can highly recommend Stockholm Tar it seals, protects and keeps fly's off.