How can you protect your circuit from unwanted magnetic or electric field?

Answer 1

put it in a metal case to avoid magnetic fields. ground it to stop electric field..

Answer 2

Terminate your grounds at one point to prevent loops and shield the circuitry with a grounded, magnetic metal covering. Carefully route any wiring to prevent unwanted capacitance. Use shielded cable where necessary.
That should do it.

Answer 3

You could always shield it, like put it in a metal case or something.

Or just keep unwanted fields away.