Smelling the food is a good start, but botulism is like iocaine powder- it's odorless and tasteless. If you see mold in your jars, you can bet that the seal has been broken somehow. You'll also want to check your jars before you begin canning; the tiniest chip in the rim can mean lost food.
I have read on the internet that the amount of heat required for killing possible botulism toxins is the equivalent of boiling the food at a hard boil, for twenty minutes. I can't verify this, but I can check with the various county extension offices and see what they say.
This is an excellent site for safe canning protocols: http://nchfp.uga.edu/publications/pu...ions_usda.html
I haven't gone over everything there yet, but what I've read so far makes a lot of sense.