generally lots of riders are quite used to ignoring signs and going where they like.
If it is a group of cyclists maintaining cyclingling trails you need to differentiate yourselves from grump landowners etc.
rather than “Trail Closed” you would have more success with me by doing:
Unfortunatly due to weather/overuse etc this trail had to be closed..
it has a number of deep bogs which are dangerous…
please use the alternative route signposted
(left, next right, etc)
Thanks
Trail maintainance guys
also bear in mind alot of riders wont know what alternatives there are, ‘thats the way i always go..’ etc
ok so you have done all that, Shoot them