Mirrors have been used in outdoor design for at least two centuries - Humphry Repton wrote about their use. The old mirrors have not survived because the silvering process was not weather-resistent. Modern mirror-coatings are much tougher and alternatives to glass mirrors are available:
Garden mirrors bring light into dark corners and can increase the apparent extent of a space.
I found an internet company doing mirrors from polished stainless, www.metalmental.co.uk
Numerous quality designs, laser cut in the shape of birds, animals, fish. Totally amazing, unbreakable and easily maintained
Your acrylic mirrors aren't big enough for use in the garden. I'd be looking for something like 32"W x 48"L.
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