You get 4 hours of lock (automatic on capture), then they can take them over.
Things you can do:
- create a wave just before it unlocks where you take out all adjacent tiles it could be attacked from thereby buying you at least 4 more hours. then when those are about to expire take out their neighbors. eventually you'll run into someone's HQ and then the wave will be broken

other guilds racing you on the next layer could also mess it up. But on a 1-dominant-guild map you can keep this going against them for a good while to make your points last longer before they run it all over again.
- build things to make it take more hits or cost more attrition to take (seldom will stop anyone and the more attrition option may piss them off and make them target you more)
- accept that you're just going to have to take it back over and over again. it is what GBG is.