Use Dorje and Bell counters.
From the above picture, you will see there are two counters made of colourful strings, 10 counter beads and a dorje or bell (the most common Tibetan Buddhist sacred ritual objects) on each attached to your mala.. Counting with Dorje and Bell When counting very large numbers of mantra recitations, it is helpful to have some additional counters attached to your malas. One of the strings has the dorje at the end, and the other the bell. Where these strings are placed on the mala is totally up to you. Tibetans usually have theirs after the 6th bead on either side of the guru bead, but that is for no special reason and you can put them wherever you like.
We use the dorje counter to keep count of each circuit of 100 that we make on the mala. So each time you finish one circuit, you will pull forward one bead on the dorje counter to the top of the counter. After 10 circuits of the mala, you will have moved all 10 beads on your dorje counter, and you will have recited 1000 mantras. After that, you will move one bead forward to the top on the bell counter, to symbolize 1000 mantras counted. Then you begin again with a new circuit on your mala, and once you have made a new circuit, you move one of the dorje counter beads forward, and continue like this. With a dorje and bell counter, you can count up to 10,000 mantra recitations.
Use Bum counter
To count 10,000 mantra recitations, we use the bum counter. After finish the first 10,000 mantra recitations, you put the bum counter after the first bead next to the guru bead. After finish the second 10,000 recitations, take off the bum counter and put it after the second bead...and continue like this.