Free radio,
No, a rhombic wouldn't be a good choice for an 'all
band' antenna. I think a better choice would be several
antennas optimized for particular bands, as high as you
can get them. But, since you rule out towers, and I've
no idea what trees you may have on the property, the
multi-antenna thingy may not be a good choice either.
Lots of help, huh?
'Doc

PS - The large horizontal loop idea isn't a bad one...