defending your empire's borders: what do you do?

[Will]

Large satellite stacks on warps, concentrated around the choke-points first, then all warp points within my space. Rotate older satellites out to the borders, and have newer designs produced both on borders and deep inside.

Big fighter stacks (usually 100), and several carriers dedicated solely to ferrying fighters from one system to the next. A few of these are usually enough (with satellites) to repel any AI attack.

Small fleets (no more than 15 ships) attacking targets of opportunity wherever possible. I've taken to putting a cargo container on ships and keeping some troops in them, and setting secondary strategy to capture planet.

Larger fleets always available to go into an enemy system, seal off with fighters and satellites, and proceed to destroy all enemy units and capture all planets.

Several BSY's in the core always producing ships, mothballing when they're completed. Just lost some ships? Unmothball the older designs and send them off as replacements.