Hi Amir,
For a little more fine-grain approach/not having to read a report every day, you'll need to do some analysis of lead records overall, which Marketo...is bad at. Marketo likes to look at the individual lead rather than your lead system as a whole, so it needs to be tricked into doing this sort of functionality. Thankfully, we're all tricky people here. 
Do note that you'll need to do some light development work here with either the API or webhooks (I'm just using webhooks in this example) to accomplish this, but it's something most programmers should be able to return to you, start to finish, in a couple of hours.
Let's say, for instance, you have a SLA of creating 5 leads a day. If you create less than 5, you and your colleague need to be notified. Create an internal lead (with a fake email address like leadcounter@mycompany.tld), then make a custom Marketo Score field called "Lead Counter." I stress making the field a score field, as that's the only reliable way to do mathematical analysis against anything in Marketo.
Set up a smart campaign to trigger every time a lead is created, then have the flow action call a webhook. Hard-code the webhook to look up the email address leadcounter@mycompany.tld and add +1 to the score field.
From there, set a batch campaign to run once a night with the smart list criteria of email address is leadcounter@mycompany.tld, Lead Counter score is less than 5. Have the flow send an alert email (with the Lead Counter score added to the alert to see if you got 4 leads vs. just 1), put a wait step for a few minutes, then alter the score back to zero. This way, you should only be notified when leads dip under a threshold and will stay evergreen in terms of alerts.