I would probably stay away from flatheads unless you have a bullhead issue, they are fish eating machines that are not very gape size limited in what they could potentially eat. Once flatheads get big they could eat the largest LMB in your pond. Even if you do have a bullhead issue I would consider trying some othter removal methods first.

Bohemian Alps? I'm not familar with that area around Lincoln.

If it were me I would try to do some preliminary sampling with a rod & reel using an ultra lite, 4-6 lb test, using a 1/64th or 1/32 oz jig tipped with a small peice of night crawler. This is one of Condello's favorite rigs and it will catch all sorts of fish in various sizes. This method does tend to work better in clearer water vs. much muddier water.