What's the rationale of Koenig lookup?
Cannot avoid thinking of it like something that makes your code a lot harder to read and more instable.
Couldn't they define Koenig lookup so that it only work for specific cases (ie: non-member operators) or when explicitly required?
The original motivation, IIRC, was to be able to write
std::cout << 42;
without having to qualify std::operator<<(std::ostream&, int) explicitely.
If you want to disable argument dependant lookup, you can explicitely qualify the function name, ie. use std::swap instead of swap to prevent swap to be looked up in whatever namespace its arguments would live.
ADL can also be used with SFINAE to test at compile time whether some function is defined for a particular type (I'll let you work this out as an exercise, there is at least one question about this on Stackoverflow).