You could set the settings as described here so that guard only logs on :error
with something like in addition you could use only or except to give you nothing actually being created:
logger level: :error,
only: []
However, as pointed out by fotanus, logrotate is the standard way of dealing with these logfiles and the way I would go about adressing the problem.
There are several different tutorials on how to use this to help manage your logging.