Set a normal trail, but for the message sign, create a message using a QR code for the cubs to remember a 6 digit number.
QR code readers(free on smartphone) One for each six
Set of message codes - best laminated
Set of answer codes
Trail signs instructions
Make sure your Leader/YL's have a code reader on their smart phone. One for each six.
Use download or create your own code to suit the abilities/sense of humour of your group
Send out the YLs (or one six) to lay the trail and use the message sign to enable the followers to find the message. I laminated mine to keep them readable.
Bluetac the possible answer codes in the hall and make sure a leader is present when they have chosen what they think is the answer.
We award points each night for inspection, behaviour and games and then give the winning six sweet money at the end of each term, which is why my codes refer to points. You can easily create codes on www.goqr.me