Despite the dismal British weather, Zac's posters to promote the search for Alice are on plain paper, not laminated or even in waterproof sleeves. They would not last more than a few rain showers.
Zac is shown wading through deep bracken to get to the canal. For visibility, his posters would need to be close to bridges, locks or pubs near the canal, all of which are easily accessible from roads or towpaths.