Frankeslot Guard rails
The standard Carrera guard rails are not that realistic. I therefore use guard rails from Frankenslot. They are super realistic. You could also use these guard rails as a base and easily build fences on them if you like. Picture above is from Slotcar-Factory.de/Frankenslot.
Barriers
Jaspeed Barriers
These 50 cm barriers are a great option. I’m using the plexiglass Jaspeed barriers on crossings. They also sell clips for those barriers.
Wimshop Barriers
On some of my curves I use their 6 cm high bands as a a guard rails. They offer 4 cm as well. They come with sponsor-stickers. You need some sort of clips. I have bought mine clips from Benzerath (see below), which are great for this purpose.
Benzerath Barriers
They are red and comes in different heights (3, 5, 9 cm) and you could add a covering band on top of them. Have a look yourself on their site. Again, you need som sort of clips.
Fences
I have used fences with mesh, from Slotcar Royale, the Minnesota based company, which unfortunately has folded. Their products were incredibly good. Now I’m using a mix of those fences from Slotcar Royale that I got left and my own made. See DIY – Fences page.