The spell components in 5e is chalk and a year of casting to create a permanent teleportation circle. The players came across a teleportation circle that belongs to an enemy wizard. They have no wizards in the party and decided to shoot the sigils in the middle of battle with a shot gun like gun. (Steam punk campaign mixing wizardry with firearms! Ha!)

So really 3 issues here:

1. Can a year of wizard's work be destroyed by simply vandalizing and rubbing the chalk off the floor or the object?

2. Can shooting hundreds of pellets into the cigils - defacing them destroy the circle's capability to teleport as the Wizard is fleeing battle?

3. After the battle if carved on stone could some dwarves with a pickaxe destroy the circle or could the circle be buried in stone so when people teleport into it they teleport into a stone wall?

I like the freedom of 5e, but, I look at it both ways, if PCs ever get to the point of having access to use teleportation circles, they're going to regret destroying them....

Thoughts on what others have done for this?