Hi,
allthough your provided code is almost unusable (it has nothing to do with XAML, where "border", "grid" and most of the other elements you listed don't exist), the solution to your wish ("menuUserControl should be seen on top") is to set
DockPanel.Dock="Top"
in the definition of menueusercontrol1.
Unfortunately I have no idea, what you mean by "calling from menu button" as none of your buttons has a command or code behind and controls aren't called. So maybe you elaborate a bit on that, if there still is a problem.
Cheers
Jürgen