The trick is to avoid having your causal help classified as an employee in the first place. Where possible do not have the same person work for you more than 2 days a week and for 6 or fewer hours at a time. If you are able, allow them to pick which days they wish to do chores for you. Be flexible with starting and finishing times. Preferably agree that you will not be providing meals for them and they will need to bring their own lunch and you will allow them the time to eat it.
Try to avoid the claim that you set rigid hours of work so that that your casual helper is unable to take on other work as it becomes available because they must be at your house.
SD is a long way to go for what amounts to 12 hours a week. I'd suggest you give the gardener 2 weeks notice and on his last day, pay him as you normally do and then give the equivalent of three weeks pay. Call it termination pay/Vacation pay - In your case, 36 hours, not a lot of money for a gringo all things considered.
If having someone at your house after giving them two weeks notice makes you uncomfortable, pay them for 5 weeks work on their last day, and be done with it. Treat people fairly and with respect and maybe they will not feel slighted and will be inclined to reciprocate. Give someone the impression that they can get more another way and you can't blame them for trying.
If you would prefer not to deal with employee hassles, don't create the situation where "the casual help" becomes an employee.