[RyanN]

A gyro can be used, but drift must be accounted for if used over the entire match.

A magnetometer (compass) would work as well, but you should consider high current electronics, motors, ferrous metal, overhead metal objects, rebar in concrete, etc...

I tried to use a magnetometer in 2008 Overdrive. It was the biggest headache... I then tried a magnetometer to orient an antenna tracking system for my school's UAS team, and the motors in the servos threw it off.

My recommendation is to avoid magnetometers at all cost, and try to implement a gyro.