Guardian of faith says:
The guardian vanishes when it has dealt a total of 60 damage.
Because of this, could you:
Have the guardian attack something with a good Dex save
Assume the thing succeeds
If not, attack it again (it succeeds, the Guardian dealt 30 damage)
Attack an object twice because objects fail Dex saves
Conclusion (4.5): The Guardian has dealt 70 damage. This means it can never do a total of 60 damage. You now have a guardian for the rest of 8 hours.
- Repeat daily
Actual conclusion: You have a permanent guardian of faith.
Would this work?