That is becoming a problem:
I've got two large turntables that holds about 30 engines, each. I've got some rail out so I can 'spike' about 5-8 more stalls for one round house. The other is full.
I've been putting the non-GN engines on some in-bound/out-bound tracks. I've got 3 in each yard and they usually are not all needed so one in each yard has been a 'ready' track for engines. The yards are 20' and 25' long so they can hold quite a few engines.
Fortunately, there's only a couple more engines that I want: a C&O 2-6-6-2 and a SP 2-8-8-2 cab forward with the whale back tender. I need to quite buying anymore engines. The problem is last century's brass is so cheap, it's hard to resist.