It may have changed since but about 10 years ago once an newly ordained monk received his monk papers he could get a 1 year visa and would be expected to report to immigration every 3 months to prove he was still a monk.
Before that it was much easier, but men had been ordaining to get a long visa then disrobing and continuing to use the visa, so monks who have been in Thailand longer than that probably have better conditions.
"Right effort is effort with wisdom. Because where there is wisdom, there is interest. The desire to know something is wisdom at work. Being mindful is not difficult. But it’s difficult to be continuously aware. For that you need right effort. But it does not require a great deal of energy. It’s relaxed perseverance in reminding yourself to be aware. When you are aware, wisdom unfolds naturally, and there is still more interest." - Sayadaw U Tejaniya