Guns of Glory Best Guards are going to be the strongest units that you can come by. This will depend on how far you are in the game and how many different units that you have unlocked. Your also going to want as man as possible for the biggest possible defense.
Having units that are stronger against certain enemies are a must. Many times when people attack you they are coming from a long ways away so they will use horse units or other things that are fast. You can be ready for them by having those units weaknesses. The best thing to do is switch your players after you see that someone is sending troops to attack your location.
Joining an alliance can be very helpful when it comes to protecting your stuff. Many times someone might back off if they notice your in a group and sometimes you might get help from your alliance with a little revenge. With this in mind you might not want to start problems with people to keep the enemy count down. With games like these if you end up being a target by other groups you could have a hard time progressing in the game.
Since guards will depend on how far you are in the game you might not want to leave anyone for protect early on as they can be removed and defeated very fast making it harder to keep up your army. It can be a waste to keep guards if you are constantly being attacked by someone who you know will defeat you.
If your having a hard time with attackers you can always move you location to somewhere new though this could also be worse off. If you have a chance to move where you want to you might consider a place right next to your strongest alliance member sot hey may be more helpful.