Something that is just as fast (slightly faster) than use constant, that can be localized, and that is neat, is to create a reference or alias to a non modifiable variable. Try this:

 
local *CONST = \23.34234334234;
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Try to modify it. You can't. Declare it at the top of your program and it is there for life. Put it in a sub and it stays around for the life of the sub. See 75935 buried way at the bottom of this node.

my @a=qw(random brilliant braindead); print $a[rand(@a)];