With planning.

You visit the mayor while the celebrations were starting, and tell him “The cliff is actually a possible weak spot in our defenses. We can see attackers before they reach us above ground everywhere else.”

The mayor nodded. “What’s your plan?”

You smile. “Build some strong walls there and bring up stones we can use to roll down the cliff. The Treant will get anything that walls there. We might be able to cut a deal with it where it protects that area, and we let it have our sewage as fertilizer.”

The mayor grinned at that, “And solving yet another potential issue of ours. I’ll have someone look into it.”

You head over to the foreman from before and sell him your stone units for a total of 3 silver pieces.

Now you can relax, leading the girls to a tavern.