In fact...I recall more or less exactly that being the scenario in Storm Front--Harry runs to his circle in his basement to get away from the toad demon but it's covered with crap and he can't activate it.
Not quite. Harry runs to his circle and cleans it off and empowers it with his will with himself and Susan inside. But that leaves him trapped in a circle. To get out he had to bargain with Bob to toss him the escape potion. He had to break the circle to catch it and quickly share the potion with Susan to escape.
I went to the far end of my lab table and started kicking boxes, bags, notebooks, and old paperbacks off the floor. “Help me clear this floor space. Hurry!”
She did, and I cursed the lack of cleaning skills that had left this end of the lab such a mess. I was struggling to get to the circle I had laid in the floor, a perfect ring of copper, an unbroken loop in the concrete that could be empowered to hold a demon in-or out.
...
I heaved a bunch of empty cardboard boxes aside as Susan frantically tossed some papers away, exposing the entirety of the copper ring, about three feet across. I took her hand and stepped into the circle, drawing her close to me.
...
I leaned down, touched the circle with the tip of my staff, and willed power into it, to shut the creature out. The circle sprang up around us, a silent and invisible tension in the air.
Something splattered and hissed against the air a few inches from my face. I looked up to see dark, sputtering acid slithering off the invisible shield the circle’s power provided us. Half a second earlier and it would have eaten my face off. Cheery thought.
I tried to catch my breath, stand straight, and not let any part of me extend outside the circle, which would break its circuit and negate its power. My arms were shaking and my legs felt weak. Susan, too, was visibly trembling.
The demon stalked over to us. I could see it clearly in the light of my staff, and I wished that I couldn’t. It was horribly ugly, misshapen, foul, heavily muscled, and I compared it to a toad only because I knew of nothing else that even remotely approached a description of it. It glared at us and drove a fist at the circle’s shield. It rebounded in a shower of blue sparks, and the thing hissed, a horrible and windy sound.