I'm sorry I was late responding to this post.
I hope your class went well.
Some of the novice mistakes I can think of are ...
1) Thinking that they can adjust the liner after there's water in the pond. (I'll just pick it up and tug it into place ... WRONG!)
2) Matching the right size pump to the right size pond.
3) Understanding that if rocks are going to be used to conceal the lining, that the rocks need to be stable. Big squarish rocks are the best foundation since round rocks tend to roll. It helps if there's an incline to the pond to help support the rocks.
4) Understanding that algae turns water green and that there are several options to clarifying the water that don't include pouring in a ton of chlorine.
5) Understanding how to clean a pond. My veggies love the muck I get from the koi and goldfish.
6) Explanation of what a filter is, what types of filters there are, and why the filter is your friend.
7) Explaining how ponds connect to filters ... or is it the other way around? :icon_rolleyes:
8) Explaining the concept of water flow with regards to water filter and pump placement.
9) A general reminder that stagnant water invites mosquitoes to breed. Mosquitoes are not our friends.