I have heard that if you (a thai national) own a piece of land and have all the right papers, if you don't use it yourself but let t.ex. a neighbour use it, then after 5 years your neighbour may claim the land, and it is simply taken away from you.

Can anyone tell me if this is true?

This certainly not true if the property has a full land title deed (chanood), a Confirmed certificate of use (Ngor Sor Saam Gor) or a Certificate of use (Ngor Sor Saam)

Not sure on the other deeds which are existing though, but one would be rather daft buying or investing in such plots without proper documentation!

They don't suddenly become "owner" of the land but there are some squatter laws that say if you allow them to use the land uninterrupted for 10 years, you have to let them stay (and either way, they can't sell it or anything crazy like that). If worse came to worse, there are no squatters that one couldn't remove forcibly (ala Soi 10), so IMO the law is pretty much moot.

Depending on the location of the land.... land owners get around this law by either a) letting the squatter farm the land (no profit, no rent paid) renting it out to whoever wants to live there (under contract) for very low rent c) simply fencing off the land and putting up a for lease sign c) is usually what I opt for, but you still have to make the rounds and check on your fences once in awhile as they'll rust and decay naturally over time (if parts of them aren't stolen). For lots in the middle of nowhere, stakes and a sign is plenty... but again, a once a year visit (with a friendly "you're on my property, you're welcome to stay, just make sure you don't move the stakes or signs and do NOT build anything that is going to take more than 1 day to dismantle if we need to use the land") is the norm.

Thank you both for your replies,

The land in question does have a proper chanood, so I suppose it will be alright.