LATE GAME PINK WARDS/ COUNTER INVIS ITEMS

So basically, during earlier and middle game, you can buy pink wards to counter invisible champions like or . But after about 30 minutes into the game, you run out of item slots for a pink ward, leaving you with only the Red Trinket, but that doesn't let you to attack the invis enemy champion. We need a way to counter these champions for late game since Red Trinket doesn't do the job. Maybe like an extra slot that can be bought, reserved only for pinks or consumables, at level 16? Please help us fight against late game invisible champion, spells, etc.................. ^^ THANK YOU!