Answer: One way to mark two measures for repeat is to use the method recommended by Gardner Read in his manual of music notation: a repeat sign that lies across a barline, like this:

That effect was achieved in our software by putting invisible rests in measures 3 and 4, then a repeat sign in bar four with its spacing set to overlap the previous bar line.

The repeat sign in this case could also have two slashes, though in Ars Nova's software the available symbol has one. Either is acceptable. However, you might want to consider whether this kind of indication really makes sense when using a computer to do notation. It is a great shortcut when writing something by hand, but is actually more work on the computer than a mere cut-and-paste or a repeat mark like those below, and it's hard to imagine it being easier to read. I'm showing you all the alternatives just to be pedantic.

If the repeated section is more than two measures, another sign sometimes used is a bracket over the section with the word "bis" (twice):

Still, I can't see why either of the above indications has any advantage over the old standard double repeat bars you mentioned:

You could also just write out the repeated passage. Unless there's a need to conserve space that is sometimes the easiest for the reader.