When you cut a pill bottle , leave the margins raised. Don't cut it all the way in.
It will help you dig in moist, sandy, but not tougher media.
If you want to dig in a tougher media from your pot, use a more tougher plastic.
1 was used first by making a hole and 2 after that. You can use 2 only.
A, B and C must have a few mm raised margins. The margins remained (red arrows too) have a straight edge.
I kept the cap for a better grip.