Squeak Interception Messages

I am trying to understand the best reflection in Smalltalk. I am using the latest version of Squeak (v4.3). I want to intercept every message sent to instances of one of my classes. I suggested that I could override the method ProtoObject>>withArgs:executeMethod, but Stéphane Ducasse explained to me that for performance reasons this method is not used (this is my own summary of its answer). What method should I override / how to intercept sent messages?

Here is the code for my attempt:

Object subclass: #C
    instanceVariableNames: 'i'
    classVariableNames: ''
    poolDictionaries: ''
    category: 'CSE3009'.

C class compile: 'newWithi: anInt
    ^(self new) i: anInt ; yourself.'.

C compile: 'withArgs: someArgs executeMethod: aMethod
    Transcript show: ''Caught: ''.
    ^ super withArgs: someArgs executeMethod aMethod.'.

C compile: 'foo: aText
    Transcript show: aText.
    Transcript show: i.
    Transcript cr.'.

C compile: 'i: anInt
    i := anInt.'.

o := C newWithi: 42.
o foo: 'This is foo: '.

Executing all of this code snippet yields:

This is foo: 42

When I would like to have:

Caught: This is foo: 42