michinyon:
How will you drive a robot if there are a couple of magnetic object on the ground
To be successful, you are probably going to have to improve your understanding of what you are actually want to detect.
Magnets ?
Pieces of iron that respond to magnets ?
Other objects ( mostly metals ), which are electrically conductive ?
Yes, I want to detect a magnet that I will put on the ground. The robot will have a ground clearance so that the magnet can go under it.