The landscape designer can upgrade decos using either dollars (bad move), deco parts (greatest move ever, thanks GGS!) or gold (only for the wealthy). She is available on all 3 main farms. Deco parts can be obtained by breaking up existing decos in storage, on your farm or in your drop box.
We like this event a lot. Almost as much as we like the architect.
The 300 gold bonus for the next 4 dismantlings however isn't that cost effective. You can get the equivalent parts cheaper just buying with gold.