People like to slag off training, some people on here at every opportunity (and you are not one FA), and I reckon it's just a hidden reason for the slagger to tell the world how much better they are than the rest of 'em. Funny that the people who slag instructors off don't have an instructor rating (though we know what other ratings they have, as they tell us - repeatedly).
I've sent students off on cross countries next to very busy airspace and I have no problem with that, and they don't have GPS. Why am I fine with that?
1) Because the 'stay out' airspace is small and so the edges short.
2) The edges are easily known, that's because whenever possible they use visual references on the ground to deliniate the airspace. It was designed with VFR pilots in mind.
3) These visual references are shown on the chart, and lots of other stuff which isn't important is not.
4) They are trained to look out of the window, and not at a GPS in the panel.
These are student pilots for god's sake, no experience whatsover. Don't tell me you need a CPL and IR to avoid busting airspace, that's rubbish. Make the airspace work for everybody and you'll get a reduction in infringements.