Mc mobs about which blocks?

So I'm building a fence in minecraft and I have a gate and I actually want to leave it open so not a real gate but built myself and then I asked myself if there's a block where monsters can't come over but you even just about it

No my friend doesn't eat. Possibly with comant bloc. Alternatively, you could explore a waterfall that distracts mobs or; a 2 block wide live ditch that you aksnt jump over

Argh thanks

You could make a normal fence around it and put another block like stone or wood on it and put a ladder on the side in the direction of the fence. Then you can jump on the ladder and climb over it, but mobs can't.