Using :type slot option

I understand that the Common Lisp standard specifies that "The consequences of attempting to store in a slot a value that does not satisfy the type of the slot are undefined.”. 

However, I am wondering if there is a simpler way to implement slot type checking than the code I wrote (see file attached). 

A small annoyance with this code is that one need to always include:
	1) inheritance to a class that verify slot types when an instance is initialized (however this can be done once for the most general class), 
	2) the metaclass option to verify a slot type when the slot value is set, and possibly (has to be done for every class definition), 
	3) the class option :optimize-slot-access nil (has to be done for every class definition), if one also wants to verify the type of a slot when it is set using an accessor.

Thanks for any suggestions. 

Bruno