The best way to tell if gates are open is if you lose scouts when scouting a city. Also due to the recent updates the basic recommendation for fortifications is greatly increased. As I saw in a previous post 3K archer towers are a seemingly feeble defense. My recommendation to my new players is to have a minimum of 5K archer towers. And the upgrades to the rockfalls have drastically changed their value as a defense. Just look at the range! They have roughly 250% of the range of archer towers not.