You have to take a closer look at the line-of-sight/line-of-effect rules to see what cover can help you with. It may prevent a caster from targeting or grant a bonus to a reflex save occasionally.
Sounds like it could block one attack per round. You get only a single swift/immediate action per round, so you may not be able to do so or wish to use it otherwise.
There are two ways to read this, amusingly.
One is, indeed, "lolnope" once per round using an immediate action.
The other is that it only works against attacks made against you where the attacking character has used an immediate or swift action to make the attack.
For the record, it's clearly the first one.
|
Read the rules for the tower shield, the total cover it provides is covered there:
This massive wooden shield is nearly as tall as its user. In most situations, it provides the indicated shield bonus to your AC. As a standard action, however, you can use a tower shield to grant you total cover until the beginning of your next turn. When using a tower shield in this way, you must choose one edge of your space. That edge is treated as a solid wall for attacks targeting you only. You gain total cover for attacks that pass through this edge and no cover for attacks that do not pass through this edge (see cover, Core Rulebook 195). The shield does not, however, provide cover against targeted spells; a spellcaster can cast a spell on you by targeting the shield you are holding. You cannot bash with a tower shield, nor can you use your shield hand for anything else.
When employing a tower shield in combat, you take a –2 penalty on attack rolls because of the shield’s encumbrance.
bold is mine.
Tower shield granted total cover doesn't block targeted spells.