Buster, I think you might be misreading this. What I'm suggesting doesn't require any long-term garrisoning of towns as you use in your example. I'm suggesting an "all ack down" period of about 10 minutes at a newly captured field. This isn't going to create a huge chain of fields that needs to be guarded for extended periods.
The idea is simply meant to extend the battle over a newly captured field by having a brief period where that field may be vulnerable to counter-attack/re-capture. It doesn't make the process of actually capturing fields any harder. It just adds that brief period where some defensive-mindedness may be needed to hold it. As it is, once a field is captured, the base-rolling horde typically just all land as a group and move on the next hording field. With this ack down period in effect, they can still do that if they wish, but risk someone recapturing their field. Essentially I'm talking about adding about 10 minutes of defense to the process, not something that is likely going to grind into a stalemate as you suggest.
Even in an extreme case, where this short "all ack down time" might actually create a back-and-forth battle of recapturing of a given field, I seriously think it is not a "stalemate" that anyone is going to complain about. It's more likely going to be a really exiting fight going on -- a fight that players with a variety of play styles could all enjoy. The "base-takers" on both sides get something out of it (as they are fighting over capturing a base), the "defenders" have a little more time to rally and get involved, and even the "furballers" who don't care about the disposition of the field may have a nice protracted fight to join into.
I don't see this happening very often, and I certainly don't see it turning into the slow-paced stalemate you describe. Actually, I see this potentially creating some epic battles. I can't see how something that potentially creates an epic, drawn-out battle every once in a while is bad for the game.
The "instantly-popping side-switching ack" upon field capture is very gamey in my opinion, and worse, it contributes to the smash-and-grab vs. whack a mole game game play that we have. Addressing that with something as simple as an ack setting that keeps a field "in play" for another 10 minutes is supposed to be an easy idea aimed at creating better fights in the main arena.
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