Seamless array of textures

I'm making a game, and I need a big field, with a material on it. I need the material, to repeat itself over and over, but when i did it, the field looked awful, it was seamless, but you could clearly see the repeating pattern. I want to make an array of material, basically a texturesheet, that has at minimum 4 different textures, that are seamless with eachother, so I could randomize it. How could I do it.

Edit: I'm using GIMP

 

Having four textures that are seamless with each other would be extremely difficult, and you would still end up with a visible repetition pattern. Your best shot is to use unity's terrain painting tools and create the texture yourself, or use an external 3D painting application to do it, like MARI, Photoshop or something similar.

 

It is diddicult, but it would get rid of the pattern effect, take a look at Minecraft, it implemented rotated textures, and the patterns are gone.