What adhesive is best for attaching polyethylene to glass? I've come up with an idea, but everything I've used?

so far only adheres for a month or less. The product I'm trying to develop is being used (by a friend who owns a business) already, and his customer's (and he) are advising me that the "feet" keep coming unattached from the glass over just a short period of time. Any suggestions, please?