The problem with LPI is that most of them are just very low power,
continuous-wave radars with a huge chunk of signal processing gear
tacked on. Smaller output, harder detection, right?

As long as you use radar,or any kind of EM energy as a binary detection
method,right.
But if you start processing,for example, polarimetric data,you can easily
seperate signals reflected by man made objects from the others.