I've beaten the pussy diggers in my garden by putting wire netting or an old barbeque grill over freshly dug soil. It can be removed as the plants start to fill out. It also foils the blackbirds, great diggers also. As my cats are indoors-outdoors I haven't had any particular problems with house plants, not like a friend of mine who has given up putting up a Christmas tree because of climbing Mitzi.
RE: MITZI AND THE TREE, JUST USE PAPER, CARDBOARD ORNAMENTS ON THE LOWEST BRANCHES. WE LOOSE INTEREST AS THEY ARE NOT SHINY. COURSE IF THE KITTEN WANTS TO TRIM HER/HIS CLAWS BY CLIMBING A TREE, YOU ARE STILL OUT OF LUCK. I HAD TO TIE MY TREE TO THE FIREPLACE. AT LEAST IT WON'T FALL OVER.