Good point, Le P.
Around where we are a number of the frequencies are affected by interference and some are NOTAMed as not being monitored by centre, but the boundaries are clearly marked on the charts (not sure what Dick's on about saying they're not), and aircraft can talk to one another.
If you're flogging around below 5000 as many of us do, there is f all chance of getting a mayday out on VHF anyway over the majority of the country.
How to fix it? Maybe mandate a GPS / satellite based surveillance system eh?!