Sorry for title, I would like to try to train my two to use just one section of the garden for toileting

Pooh corner, brought the jelly like pellets that are supposed to repell them from using that part of the ground. But Indi I'm sure just pee'd in between the pellets I have tried just taking them to the area where I want them to go they do usually pee comand but when I'm not there they just go where they want. Suggestions and magic wand needed.
Thanks
P.S. forgot to say they are 2 and 3 years old