Answer:
It's in your hand though you can not feel it. Only you and time can reveal it.
A mighty weapon in the war against winged household pests.
To unravel me you need a simple key, no key that was made by locksmith's hand. But a key that only I will understand.
Man walks over, and man swims under. In times of war, it can be burned asunder. What is it?
He has married many women but has never married.
People take me on walks and I run and have fun. What am I?