A lot of those I linked would be an "underground wiring" sorta deal... Just get the appropriate outdoor/underground speaker wire.
The non-rock looking ones that sorta have a "trash can" look to them I have heard before and they sound surprisingly good. Not great, but not terrible. They'd work well hidden behind bushes or mixed in with the landscaping somehow like that...
They had a nice "omni" like dispersion of sound for lack of a better term, really threw the music out there despite their less then ideal location in the garden bed