defconstant vs. lexical variables

[OLDMAN@USC-ISI.ARPA]

Page 69 of the CLM states:

"Once a name has been declared by defconstant to be constant, any
further assignment to or binding of that special variable is an
error.  ...  A compiler may also choose to issue warnings about
bindings of the lexical variable of the same name."

Question: How can I make a lexical binding of the thing if it's
implicitly proclaimed special by the defconstant?

Alternate question: Why don't we have a way of declaring
something locally lexical?

--Dan Oldman {Data General}