If my base is undervalued attack, what’s best solution so I don’t lose troops?

If you are attacked and you don't want to lose troops then the best solution is to send them away. Send them to reinforce the base of an alliance member. Or send them to gather at a plot far away. Or attack a zombie on the other side of the state for example. You may lose resources from your base but your troops will be safe. If you have any left over troops that don't fit in your APC's then they will remain at the base and be vulnerable.

The other options are to use a peace shield item to protect yourself from any attack or a teleport item to move your base somewhere else. There will cost diamonds to purchase though if you don't have any.

You can remove resources from roads to prevent loss during an attack, but any resources or money listed along the top can be taken during another player’s raid. The best solution is to only keep what you use, say for a building upgrade, so they get little to nothing if they raid you.