I don't much like the concept of using a shield in a metaphysical battle: by thinking there is something you need to distance yourself from, you sow the seeds of your own defeat.
Nevertheless, by looking from a different perspective, shields can be interesting.
Let's take a look at the following shield types:
A wall is simply a shield (or a multitude of them) used unconsciously.
Whether used inside or outside oneself, walls are good for one thing and one thing only: giving the illusion of safety.
Ignorance is bliss, but if your goal is anything else, cut through and burn your walls as soon as possible.
A cocoon is used in non-battle situations. Cocoons are most famously used in rituals of initiation.
A cocoon is the ultimate shield, fearsome it its use. By shielding from everything, you shield from nothing.
The insignificant outer demons ('walls', actually) are quieted, and the inner demons appear in full strength.
You see yourself and accept the responsibility of being yourself - or you summon the outer demons to shield you once again and continue living as a shell.
A cocoon is most interesting.
The darkness it represents is the quenching and equalizing water. In its most extreme form, it crushes and seals off from fire, and denies all movement - it is the status quo; a state of being stuck with a static self.
An interface allows to adjust between different structures, different frequencies.
By combining the water with structures of fire and duality, what you create can balance. What you create is suited to inter-operate with other systems. Thus, for example, you can get a grip on a blade of fire.
Interface shields are also good for proximity alarm for others ("Warning! If you come closer, this and this is going to happen to you. Make your decision.") and for equalizing energy for communication at a particular level.
Boxes are inverse shields: instead of protecting with defensive thoughts, you attack with superfluous and unclear ones.
To imprison and choke a consciousness, boxes are the way to go. Judgements, manipulation, seduction, confusion; some find these to be delicious.
There is one problem: to be able to throw filth at someone, you have to have filth within yourself first.
Boxes backfire all the time.