A fair sentence ....
Make them buy seedlings.
Make them but a trowel.
Make them hoof up each seedling, plant, water repeat.
Water throughout the summer or until the seedling is deemed viable.
Should a seedling or sprig die, they have to replace it and maintain it till it is deemed a viable tree.
Length of sentence .... when all of the growth is firmly established.
Oh! One last detail. Stabilize that area from the wash out that is bound to happen. All of that friable soil is bound to be a washed out gully.