There's a bit of a gap in the rules here for what happens when the unit carrying the plant dies before it gets a chance to plant it.
Also, some of your rules reference "the closest unit to the pond", but that's likely to be a tie between a bunch of them since nobody really wants to get near it. "A random unit" probably would've been easier, and make people less focused on staying exactly 3" away to minize chances of mishaps.