Here's another idea:
Deployed Guild Armies should grow old and age, and finally die, thereby, needing to be replaced. Guilds have deployed armies in various guild maps and have had no activity for months and maybe even a year or two. Those maps are locked up by long term guilds who will not attack each other. That's fine, but cause the long term deployed troops to fade away thru aging. That would at least cost them something to hold on to them indefinitely.
Why do you not just attack those guilds? Than their troops will fade away, no need to have to implement anything for that (and no need to wait for that either)
For the guilds burried and without landing zones that suggestion is impossible. No need to attempt it; it's not even a choice!
Aging troops is a required feature, to keep the maps, especially the old ones with locked up sectors, vibrant and moving.