magnetic geocaches

[wozza and piggynose]

what are the legalalities of sticking magnetic geocaches on lamposts

[Mad H@ter]

No different from any other type of cache or attachement method.
From the Geocaching.com guidelines 1.2:
"By submitting a cache listing, you assure us that you have adequate permission to hide your cache in the selected location."

https://www.geocaching.com/about/guidelines.aspx