Thailand has mixed English-American law type. Unfortunately Thai court would always admit rightness of Thai citizen.
Therefore carefully read and make the contracts, perfect option is using legal services agent. Agreement may be done in Thai or English language. Land lease agreements, after their registration in Land office, are not subject to rupture unilaterally.
It can be done only by mutual consent of the parties. Maximum term of the land lease agreement is 90 years (3 times by 30 years).