You can fiddle with the z values of the patch to change whether it appears on top. Z values larger than 1 will usually make the patch appear in front of quiver and values less than 1 will make the patch appear behind quiver.
Example:
[x,y] = meshgrid(0:0.2:2,0:0.2:2);
u = cos(x).*y;
v = sin(x).*y;
figure
subplot(1,2,1)
patch([0;2;0] , [0;2.5;2.5],[0;0;0],'r')
hold on;
quiver(x,y,u,v)
hold off;
title('Quiver over patch');
subplot(1,2,2)
quiver(x,y,u,v)
hold on;
patch([0;2;0] , [0;2.5;2.5],'r')
hold off;
title('Patch over quiver')
Produces:
