The only possible complication that I can see is if EVERYONE at the range is using the common ones (FRS/GMRS IIRC) ... even though they have privacy codes, that just means that you won't be interrupted by other conversations on your channel ... but you will still be interfered with if there is a lot of chatter ... meaning that if two people with different privacy codes talk on the same frequency at the same time, then nobody gets to understand anything
In that case, you'd be better served by one of the spread spectrum handsets ... I can't recall the brand name, but there is one that is not all that pricey that should work really well at that range. I just googled it ... the brand is TriSquare.
Saands