exterior vinyl siding starting to detach from the base?

exterior vinyl siding starting to detach from the base where was set.
I clicked it back but it won’t stay too long.
what should I do about it?

Should I use sheet metal or what else to prevent rain water damaging my house siding along the base?

I am ready to replace my house sidings, but wanted to make sure they don’t get damaged by rain water again easily. Should I use a layer of sheet metal along the base? Or what materials is best?