Desdinova's simple guard

You create a force field around the pointed object or a creature granting +1 to its armor class. While the shield is on target of the spell is protected from tiny projectiles, such as raindrops, snowflakes or dust as well as air moving no faster than 10 miles per hour. The user loses its concentration whenever one of the spells targets is damaged.

At Higher Levels. The number of shields avalible at the same time increases by 1 when you reach 5th level , 11th level , and 17th level .Those can exist at the same time and count collectively for the concentration however each demands its own action for cast and has its own duration of an hour.

Spell can be casted as a ritual with cast time of 10 minutes, expending the components. Doing so grants the effect of Desdinova's simple guard to numer of creatures as shown in your "At Higher Levels." note without the need of concetration.