You can target items that have sub menus and add them some right padding to make room for the sub menu indicator like this:
.main-menu ul li a.has-submenu {
padding-right:30px;
}
Or, alternatively, you could use the subIndicatorsPos: "prepend"
option and then use static position for the sub-arrow and float it to the right – something like:
.main-menu ul li a span.sub-arrow {
float:right;
background: url(/Resources/right-arrow-white.png) no-repeat center;
height: 34px;
width: 20px;
}
Or if this is just for horizontal main menu items, you could use subIndicatorsPos: "append"
and something like:
.main-menu ul li a span.sub-arrow {
display:inline-block;
background: url(/Resources/right-arrow-white.png) no-repeat center;
height: 34px;
width: 20px;
}