@Richard *****
then you have to leave every 90 days. Each time you enter until the end date on your visa you'll be stamped in for 90 days, even if you enter on the last day. One of your entries you can also apply for the 60 day visiting Thai family extension near the end of your 90 days.
You can leave and immediately return as long as you stamp out of Thailand, stamp into another country and stamp back into Thailand.
You can get Visa on arrival at Laos and you can also apply for visa on arrival online for Laos. Land and air works the same for re-entering Thailand.