On Tue, 15 Jun 2010 23:35:34 -0500, "DanG" wrote:

There is polycarbonate - Lexan is a major brand - that
is virtually indestructible. You can smash it with a sledge
hammer with no visible effect - great stuff, but it scratches
easier than the acrylic.

Lexan (bronze color) has been used in prisons (exterior cell windows)
for 30 years, depending on security levels. Those in the asylum are
not issued sledge hammers.