As far as I know, one is supposed to repair a wall to 100% in order for it to “reset” the timer and get another random deteriorating rate.
This doesnt always work, for whatever reason:
One of the walls I had kept deteriorating to less than 50% per day every day until today, when it just went down completely, every day I repaired it to 100%, so the timer shouldve reset, it didnt, it actually kept going and making the deteriorate rate worse. All my other walls are at 90-100% except for one that also went to 20% overnight so i destroyed it to build another one