Think pursuit mode but for the galaxy map.
I often end up with small groups of planets linked together on the map, and I tend to leave a fleet or 2 behind to act as a defensive force.
Receive a warning for an AI wave towards a specific planet in this linked group of planets, select defensive fleet for this group of planets, right click planet.
How about a fleet option to designate the fleet to do this automatically, essentially pursuit mode but across multiple planets.
The general function being:
Place fleet on allied planet
Designate the Fleet as a defensive fleet in its fleet window
It then automatically moves to the allied planet with the lowest immobile strength that also borders a neutral or hostile planet, or more importantly, to the allied planet with enemies currently on it.
The planet it chooses to idle on could be further improved by using the ratio of immobile strength to neighboring hostile mobile strength. Then actively watching neighboring planets with hacks or recon would actually improve your defense fleet's positioning as it has better information.
A defensive fleet will NOT cross neutral or hostile planets, so it only defends the interlinked group of planets it is currently in.
If a warning pops up for a wave targeting one of the planets in this group of planets, the defensive fleet will automatically move to that planet.
If you have wave warnings turned off, this also means that defensive fleets won't automatically move to a targeted planet.
Multiple defensive fleets will work together to cover multiple planets, so if 2 planets are being attacked, your 2 defensive fleets will defend both planets, instead of both choosing one then moving onto the next. If only one planet is being attacked and no other waves are incoming, then multiple fleets will all go to the same planet to clear the wave.
A fleet's defensive fleet designation can be removed at any time.
TLDR
It's your own little warden fleet.
