Put it in a metal enclosure and follow ESD design principles.
Use a surge arrester on the feeder. This will help with nearby strikes, but obviously not a direct hit!
It depends on many things and it’s near impossible to say without knowing a lot more about the setup. But if the system is half-duplex you can switch T/R and terminate the RX input during transmit. If it’s full duplex you can split Tx/Rx frequencies and use various types of filters to sufficiently attenuate unwanted signals.
Others may have other suggestions, but the requirement is a little vague! If you don’t have someone with RF experience on-hand to consult with, perhaps if you provide some more details here it will be easier to advise.