FREE rent. Land for permaculture project In Central Portugal

Off grid land on offer. Rent FREE. Ideally for food forest/permaculture project. The land is situated in Malpica do Tejo 20 minutes drive to Castelo Branco (Central Portugal). It is a 10 minutes drive to the village of Malpica do Tejo near the Natural Park. It has 1.4 hectares, a well and a stream. Only a few fruit trees but you can plant loads more. It has a ruin made of cob that can be rebuilt and also space for other small shelters. It is a bit isolated so its better suited to a group of people rather than one family. Plenty of water

What would be the security of tenure ? In other words what rights would the persons have to live on this land And for how long ?
I ask because an unscrupulous person might wait until someone has worked hard improved the land planted trees etc etc only to find themselves thrown off the site whilst the owner manages to sell the now improved lot he could not sell previously. It would be my worry were I to take up such an offer .

David