No docking while shield up with the possibility of shooting the base just to prevent others to dock does promote nothing but trolling.
If you want to make em hard to maintain raise how many goods are consumed or simply make shields not being undestroyable.
-raise good consuming
-make shields getting dmg
-give shields high regeneration rate
-remove "shields up = no dock" trollfeature
-allow caps to shoot blockaderunning traders during a siege 3k next to the station.