Armed groups who take physical control of a plot of land and demand payment before the owner can develop it. They act sometimes on behalf of a claimant and sometimes entirely on their own account.
Land guarding is a criminal offence under the Land Act 2020 (Act 1036).
It happens most often on undeveloped plots on the outskirts of Accra, which is one of several reasons to fence, signboard and visit land you buy rather than leaving it idle for years.
If you encounter them, do not negotiate alone and do not attempt to remove them yourself. Report to the police and involve your lawyer. The risk of physical harm is real.