Several years ago a friends of mine discovered that the empty lot across the street from their house was going to be turned into a tennis court. It took some time and we were able to "rescue" many wildflowers each year for several years. I can't remember how many trillium I transplanted (around 3), but I have had at least nine clumps blooming for the last 2 years.
Each year someone (deer? rabbit?) eat several of the flowers. The thought had crossed my mind to put out moth balls to ward them off, until I read this in The American Woodland Garden by Rick Darke:
"Each tiny seed has an edible lipid-rich appendage called an elaiosome, there only for attracting ants. Ants respond by carrying seeds to their nests, where larvae consume the elaiosomes, leaving the embryos in the seeds undamaged. The seeds are left to germinate within the ant nest or after being discarded to waste piles." I don't want to discourage the ants, so maybe I'd better leave well enough alone.
The shady bed housing these trillium contains a lot of myrtle (which you can see in the background of the photo). I have heard that myrtle will smother wildflowers, but at least two of the clumps are entirely covered by the myrtle. I also have wood poppy and even native ginger popping up through the myrtle.