One from my childhood, heard on BBC radio.

I'm Fishing!
Don't come anybody, don't come near,
I'm just afraid that the fish might hear.
He thinks I'm playing with a piece of string.
He thinks I'm another sort of, funny sort of thing.
But he doesn't know I'm Fishing.
He doesn't know I'm fishing.( sung quietly)
That's what I'm doing.( sung quietly)
Fishing1