My Suggestion for sanctuaries is the ability to start one and being able to keep it going indefinitely through FIP interactions.
Each sanctuary level will still take more FIP points to obtains but it will also need that many points to keep it at that level.
Each day, sanctuaries will drop one level but so long as players are doing enough FIP’s they regain that level. Doing more will increase past to the next level to be able to add another creature till they get to level 20.
Of course keeping a sanctuary at a higher level will take higher level creatures and more FIP’s.
If enough players are not doing their FIP’s or doing too many FIP’s on lower level creatures, they may not make up for the lost daily level and the sanctuary will loose levels.
Every alliance will be able to build and maintain a sanctuary at some level so long as everyone is participating in creature interactions. If the participation falls, so will the sanctuary level. If lower level creatures are filling a sanctuary, the level of that sanctuary will not be able to be maintained or increased.
If a sanctuary is abandoned, it will still drop one level a day till it reaches 1.
If all the slots are full when a sanctuary looses a level, the creature in the farthest last slot will be returned.
Creatures are still automatically returned after 2 days.
I think this would be a better way to do sanctuaries rather than having them expire in 2 weeks.