I used to use propylene glycol mixed with water and dry dirt. Probably find it at your local mill where farmers get their supplies. Worked good left dirt looking wet. Here is what i found for a mix rate when i googled it, can buy from trapping suppliers also.
Propylene Glycol
When using as an anti-freeze at canine sets, mix 1 part glycol with 3 parts water and spray in several layers while making the set.
