KittenKat
I've not encountered thorns. I've run across christmas tree needles people had dropped all over the pavement and they were no problem. Ultimately I can see thorns nailing you but "puncture" injuries are usually fixed the next day. I don't think I've seen anyone complaining of thorn injuries so it's not a big problem in general.
The really tiny stones are a bit annoying to start with particularly if they're the same colour as the pavement (as you can't see 'em of course). After a while you can cope with them. Larger stones you can see and step over. If where you are it's impossible to avoid bigger stones then I guess you'd have to look into "gravel bucket training" which might do the trick, I've not tried it (but it looks like that does the trick to harden your feet to such things). When I was about 6 I could run along a track made of flints to a stony beach where I'd play on barnacle covered breakwaters no problem (until I fell off one) so you can get use to most stuff. That was 40 years ago and I'm now only a few months into going barefoot again so not certain what's possible after such a gap yet.
I just hop over the poo but I guess if you step in it then it will hose off easy enough. No harder to get off than from a shoe. I seem to live on dog plop ally at the moment (and a close second for glass shard street) but so far zero barefoot incidents of note for me, 1 splinter, (but for the shod kids returning home... we practically have to hose them down by default. Arrrgh!).
I'm not committed to barefoot in some kind of uber dedicated way, I want to try it, give it a chance, see if it allows me to get back into running, see if it helps with form etc. and may be do some barefoot some shod, dunno yet. So far the barefoot experience has been very interesting and I'm very glad to have done it again, most enjoyable. All my barefoot injuries so far have been trivial except possibly one that I picked up in shoes running to a place I wanted to try barefoot in!