The guards chain aggro when you put up towers; you can have them farm balloons for you if you do it right; would that be considered exploiting? If this is a problem, then 1) remove guards ability to chain aggro; 2) remove tower ability to chain aggro; and/or 3)code the walls so nothing passes through them (flames, balloons, etc.)
And for lower guilds that cannot kill guards easily, use the catapults.
The tower guards (includes Guild Honor Guard, of course) will aggro and attack anything that a flame or electric tower attacks. This can also include "attacks" by FoTs and/or Eyes of True Knowledge, if the "target" is close enough to the tower for the guards to aggro. This is apparently intended. You will not receive merits from a balloon if the guard(s) alone kill it.
Multiple electric towers, especially after they've been upgraded one step, have their range and power extended past the nominal 450 units range. This is intended and can be quite useful for interrupting spellcaster skills and for popping characters out of Hide or Invisibility (potion or Visual Illusion tower effect.) Of course, the towers must be within range of each other, but as more towers are added to the "chain", the range is added and extended. Several years ago a video was posted showing a line of chained electric towers running from the "home" guild castle to the opponents' guild castle. Each of the towers was well within range of each other, all were single-upgraded. (It was done as an exercise by the poster's guild during a "no-show" siege.) Use your imagination here.
BTW, electric towers do
not need to be upgraded in order to remove an invisible foe from invisibility. A single, un-upgraded electric tower can be useful for revealing Rogues or anyone using an Invisibility pot far beyond the range of an Eye of True Knowledge.
Many lower-level players will set up a flame tower or three in the back areas of their castles in order to farm balloons and collect merits. This isn't an exploit or cheat.