  We analyze, by means of Melnikov method, the possibility of modifying the
threshold of homoclinic chaos in general 1-dimensional problems, by introducing
small periodic resonant modulations. We indicate in particular a prescription
in order to increase the threshold (i.e. to prevent chaos), and consider then
its application to the bistable Duffing-Holmes potential. All results are
confirmed both by numerical and by analog simulations, showing that small
modulations can in fact sensibly influence the onset of chaos.
