keyword names that can't be set in maxima

I would find it handy if I could declare certain names to be not settable.
e.g.
declare(foo,symbolic_constant)

==>
Foo:34   ==> error.

This can sort of be done (try setting %pi:22/7  for example) but I don't see
a user-version of this.  
Reason:
Previous suggestion for keyword-based arguments like this: 

Gaussianint(fun, limits=[0,inf]);

If limits were declared to be a keyword symbolic constant, it would prevent
someone from setting it, e.g. limits:hahaha,  or limits:points, and messing
up the call.

Comments?
RJF