Man you're killing it with the quick tutorials. I love it. Thanks for giving the tip with mobs being pushed across the trench. This is often an issue with these barriers.
Double thick carpet hole blocks mobs even if they happen to get shoved on top of that first carpet. You'd basically have to have a mob farm directly next to your house in order to get enough mobs trying to cram their way in. If you keep villagers in your base and are worried about the "midnight zombie siege" or whatever they're called, this method should be good enough. If you want to be EXTRA careful, leaving only 1 space above the carpet block position before having a roof or the top of the entrance (fractionally less than 2 block high space), you will actually physically block the full size zombies from even getting on the carpet, further decreasing the chance of any baby zombie or creeper getting shoved inside. You can also combine it with trap doors on the roof to further block creepers and I believe players must crouch through, similar to trapdoors above and below or a single roof/floor slab (only with the carpet method, as players can just about slip under a roof trap door)
If you have never seen a mob cross a rail, you must not have raided many mineshafts. Mobs will push each other across all the time. Stone and wood fences also don't prevent mobs from pushing each other through, but the tight space makes it very unlikely.
if you don't mind the possibility of mobs being pushed through, you can use an open trap door as an actual door that you never have to close. or two for a two block high doorway, to make sure those babies don't get through. mobs will never pathfind through it, but like i said, they can be pushed through if there are a ton of them. another great one is a piece of carpet on top of a fence. mobs don't realize they can get over it but you can easily jump on top of it since the edge of the carpet extends beyond the fence's hit box. it's possible for a mob to get over it if they're hit and bounce up and then pushed. but that's extraordinarily rare. and my last one that use regularly is a moat. you can dig a two deep hole around your house that you can easily jump, but mobs can't. i normally make the far side only one block high so you can easily get out of it yourself if you fall in.
