I noticed a few days ago that our 2 pet dogs were scratching a lot and I discovered fleas on them so they were treated with frontline. Today I was giving Barney a health check and I saw one huge flea on him, tried to catch it and get it off but it disappeared too quickly. What on earth do I do? It's definately a dog flea as it is so visible. He's nearly all white so I wondered if that's why they're attracted to him? Please help me!