The best answer of all is to conserve your building projects. I now never clear the bush until all the other puzzles have been solved. The bush can be used to train builders quickly throughout the game.

[SPOILER] Drop a villager on the bush; whenever he or she picks up an armful of leaves building skill will be gained. However, if you interrupt the villager before the leaves are delivered, and drop him/her back on the bush, no progress is made in clearing the leaves, so builders won't return to the job and complete it while you're not looking. [/SPOILER]