Hi there
One sensible way is to have an OPEN SEPARATE Wireless network (only available to people in the workplace of course) that is a basic WiFi system that isn't connected in any way whatsoever to the corporate network and allow people to use the Internet on their own devices while keeping company laptops etc that are connected via LAN's etc reasonably locked down.

Also if companies are worried about stuff being "removed" from the workplace then they shouldn't have this material available on their LANS in any case.

The BYOD is actually NOT a bad idea if implemented properly -- especially when most of the people are external consultants.

I often download basic stuff from our LAN to do presentations etc after work -- my version of Office is much more up to date than the company one -- and I can get the job done very much quicker than struggling with an old cludgy "XP" system with say Office in French or some other language I barely understand and one of those absolutely HIDEOUS French AZERTY keyboards.

Of course BYOD imposes a lot of extra work on usually overstretched IT depts. but it's usually a worthwhile effort --if you have responsible well paid external professional consultants things like viruses should not pose a mega problem (although there are always one or two "Rogue Consultants" around).