try absolutely positioning your navMenu at the bottom of the master page....

realize though that SmartPhones ignore absolutely positioning....

the normal way of doing what you are trying to do (place a nav bar at the bottom of a mobile device viewport) is done with jQuery.mobile

http://jquerymobile.com/test/docs/toolbars/docs-navbar.html

I have tried to do the same with asp.net masterpages and have since given up....

you may like to have a look at

m.moshtix.com.au

which uses asp.net for both their desktop and 'mobile' portals. woops... fairfax has closed it down...

try m.seek.com.au which uses vanilla html....

the thing is you cannont use asp.net master pages with handheld targets which do not use absolute positioning.

the preferred VS tool for mobile development is MVC 4.