My dad slides down in his wheelchair, any suggestions how to keep him upright?

There are geri chairs that the seat slants back a little so they can't get out. These chairs seem so much more comfortable. Moms was cushioned and had cushions at her head. If she fell asleep the chair could be reclined and the cushions supported her head.

Ask if there is a cushion that slants. This may help.

One of my pet peeves is seeing people left in improperly fitted wheelchairs - ask for a consult with an occupational therapist to see how to modify his chair or how to get funding for a new, custom chair.