  In a recent letter [PRL 80 (1998) 3539] Fisher, Le Doussal and Monthus report
new predictions for the persistence properties of Sinai's model, which they
obtain by using an approximate real space renormalization group scheme. In this
comment we show that these predictions can be derived in a rigorous and more
transparent way by reducing the quantities of interest to particular
statistical properties of a simple random walk in a homogeneous environment. We
also point out that they are valid in a much more general context: our results
are neither restricted to the random force model but are valid for any
asymmetric hopping model, nor to the vicinity of the critical point.
