no flies on (one)
One is very active or works at a fast past. Alludes to the idea that flies do not or cannot settle on fast-moving animals. There are certainly no flies on Judy. She works so fast that the rest of her team can't keep up with her.
(there are) no flies on somebody
(informal)
1 somebody is not stupid and therefore cannot be tricked or deceived easily: You can’t just tell her that you’ve lost the money; she’ll never believe you. There are no flies on Jane, you know.
2 somebody is skilful or clever at doing something: There are no flies on Jim. He can persuade anybody to buy a car from him.