I want to put some left litter and stuff in for my millipedes but how do I ensure is safe? I just went to pick some up that had collected next to my neighbours wall but then noticed a cat turd right in the middle of it. Unsurprisingly I've gone right off the idea now!

I've seen some millipede substrate on faunology.co.uk but by the time you add shipping it's £22 for 10ltr which seems like a complete rip of for what it is.

Suggestions welcome.