"Is there a way to cancel rentals on all of my cards?" This is another SPLEX question I've seen recently. Yesterday, 
Step 1: Go to Your Collection Page
Go to your collection page through the account overview section, through the "collection" tab from the top menu, or use the URL and replace your account name https://splex.gg/collection/@baddyeren.
Step 2: Disable Rent Golem Control
If you want to disable ALL cards from renting, use the "select all" check box in the top left corner.
Next, select the green shopping cart button at the top of the page. This will take you to the Card Caddy.
From the Card Caddy, select "Golem Control" and then the deactivate command.
Step 3: Cancel Rental Listings
Follow the same steps shown above. Go to your collection page, select all cards, and go to the Card Caddy. From the Card Caddy, hover your mouse over the "rent" button and select "Cancel Rent Listing." This will cancel all card rentals from the selected cards.
Other SPLEX Collection Filters
If you only want to cancel some of your card rentals, or do other work with your cards in the Card Caddy, the SPLEX collection page has a lot of other filters. A helpful one that
For example, using the filters below (legendary, Chaos Legion, and "other") will show only your duplicate CL legendary cards. This filter ignores the card(s) you are using to play, which makes it much easier to identify the extra cards that you may want to transfer to a rental account, sell, or combine.
I hope you found this useful. If you're trying to rent and play from the same account, I've posted some instructions for how you can do that on this article,
How to Rent and Play from the Same Account with SPLEX.
SPLEX has a lot of great free tools that I use almost every day, if you want to learn more you can read about My Favorite Free Tools from SPLEX.