Do statement local variable restriction workaround

I'm making a "Gate" block where custom illagers deal damage to it to try to break through. "Damage" is stored in a local variable inside an on block tick update where the block checks for illagers around it then it SHOULD damage itself accordingly. Since there will be multiple gate blocks, I can't just switch it to a global.  I LITTERALLY JUST NEED IT TO RETAIN THAT NUMBER INSIDE THE BLOCK FOR 15 TICKS IS THERE A WAY TO STORE A NUMBER ON A BLOCK!?