To prevent adult diapers from leaking make sure the adult diaper is not too large and make sure the adult diaper is sealing tight enough around the legs and the waist.
If the adult diaper is too big then there can be gaps between the legs which can cause leaks.
Just like with baby diapers that are too large and have gaps around the legs they can leak there as well.
So make sure the adult diaper is the right size to prevent leaks.
Also you may have some poor quality adult diapers as there are some really bad adult diapers out there.
My grandma when she was alive was wearing adult diapers for urinary incontinence and her health insurance provided her with sucky adult diapers that were really thin, the absorbent material was just wood pulp that fell apart in the diaper when she walked.
So I ordered her some adult diapers online instead and paid for them myself.
After buying some higher quality adult diapers for her she didn't have any more leaks and she was more comfortable in them.
I bought her some of those Northshore MegaMax adult diapers that are plastic backed and they are tape on adult diapers.
They are very absorbent and hold up really good.
You can also add a baby diaper such as a Pampers Baby Dry or Huggies diaper or even the Dollar General brand Gentle Steps diapers into the adult diaper as an extra absorbency pad.
Baby diapers make good adult diaper booster pads to help increase the absorbency of the adult diapers.