I was trying to make a function that determined if a program had already the correct runpath set (don't ask...) This should be possible by inspecting the _DYNAMIC symbol as show here and just looking at my own d_tag == DT_RUNPATH entry:
http://stackoverflow.com/a/2846736

However, after running a binary through patchelf, it seems like the _DYNAMIC symbol points to garbage? I haven't investigated more, but I suspect that it just isn't updating that symbol after replacing that ELF header section... if that's the case than probably some other programs that are trying to be clever with _DYNAMIC-introspection