Maybe protect the important segments of industry: The farms, metal productions, etc. Citizen homesteads could be exluded from the protection program. It also wouldn't take as long to build, and you could have a gatekeeper for each segment of industry. One for mining, one for farming.
There are two problems with that.
One, the gatekeepers would have to let people in every few seconds, considering how many people come and go throughout the industries. I do not think they would want to be gatekeepers if that was the only thing they ever had the chance to do.
Two, our entire food industry is kinda scattered throughout residential areas.
It is better that we have the gates at the outskirts of town, as there is minute amount of traffic entering and exiting the city.
And I must stress the need for multiple entrances. A gatekeeper may not find anyone to hand the claim over to, so he'll have to go to sleep without declaiming and lock us in for 12 hours or so. With multiple gatekeepers in different timezones, there would never be such long period when none can be found.
I'm not sure how multiple entrances would help in that situation.
Vucar is correct, no matter how many gates we have we would always have the same number of potential gatekeepers.