If this card attacks while in Defense Position, it is unaffected by "Mirror Force" because "Mirror Force" only destroys monsters in Attack Position. Pretty much the same idea holds true for "Spider Web", as being already in Defense Mode, it won't be changed if it attacks.
"Magnum Shield" is a good Equip Card to use with this card. It works well while it's in Attack Position and in Defense Position to have a solid wall or a solid attacker, based on what you need at the time.
"Spikeshield with Chain" is also a great card that works with "Shogun", as it will gain 500 ATK, plus another 1550 points when it battles another monster in Defense Position during damage calculation.